I'm getting the following error in PlayFab in Unity. Does anyone have any idea how to fix it? It's beyond me.

This issue seems to belong to the business category of unity, not playfab. You need to navigate to [Jobs]->[Leak Detection]->[Full Stack Traces], select it and restart unity.Then the error content in the console will be show that the memory leak occurred in the data retention location. After knowing the location of the leak, you just put the variable in Dispose, but it is recommended to enclose it in the using statement.

@Richard Berger You might need to actually include the jobs package (manually, maybe) in your manifest.json file:

"dependencies": {
  ...  
  "com.unity.jobs": "0.8.0-preview.23",
  ...
}

Depending on who reads this post and when, the actual package version may of course differ, but you should be able to update from the editor (PackageManager UI) after modifying your manifest.json (unless Unity decides to drop the package or integrate it elsewhere, of course, but then this answer will be outdated anyway...).

Actually (if it gets published) you can ignore my previous answer. While the number of memory leaks has seemingly decreased with the integration of the latest jobs package, they do still occur and seem to originate from the PlayFabUnityHttp class. At least this is what I'd conclude from the stacktrace:

A Native Collection has not been disposed, resulting in a memory leak. Allocated from:
Unity.Collections.NativeArray`1:.ctor(Byte[], Allocator) (at /Users/bokken/buildslave/unity/build/Runtime/Export/NativeArray/NativeArray.cs:69)
UnityEngine.Networking.UploadHandlerRaw:.ctor(Byte[]) (at /Users/bokken/buildslave/unity/build/Modules/UnityWebRequest/Public/UploadHandler/UploadHandler.bindings.cs:98)
PlayFab.Internal.<Post>d__12:MoveNext() (at Assets/PlayFabSDK/Shared/Internal/PlayFabHttp/PlayFabUnityHttp.cs:129)
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr) (at /Users/bokken/buildslave/unity/build/Runtime/Export/Scripting/Coroutines.cs:17)
UnityEngine.MonoBehaviour:StartCoroutineManaged2(IEnumerator)
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator) (at /Users/bokken/buildslave/unity/build/Runtime/Export/Scripting/MonoBehaviour.bindings.cs:91)
PlayFab.Internal.PlayFabUnityHttp:MakeApiCall(Object) (at Assets/PlayFabSDK/Shared/Internal/PlayFabHttp/PlayFabUnityHttp.cs:119)
PlayFab.Internal.PlayFabHttp:_MakeApiCall(String, String, PlayFabRequestCommon, AuthType, Action`1, Action`1, Object, Dictionary`2, Boolean, PlayFabAuthenticationContext, PlayFabApiSettings, IPlayFabInstanceApi) (at Assets/PlayFabSDK/Shared/Internal/PlayFabHttp/PlayFabHTTP.cs:228)
PlayFab.Internal.PlayFabHttp:MakeApiCall(String, PlayFabRequestCommon, AuthType, Action`1, Action`1, Object, Dictionary`2, PlayFabAuthenticationContext, PlayFabApiSettings, IPlayFabInstanceApi) (at Assets/PlayFabSDK/Shared/Internal/PlayFabHttp/PlayFabHTTP.cs:133)
PlayFab.PlayFabClientAPI:ReportDeviceInfo(DeviceInfoRequest, Action`1, Action`1, Object, Dictionary`2) (at Assets/PlayFabSDK/Client/PlayFabClientAPI.cs:1751)
PlayFab.Internal.PlayFabDeviceUtil:SendDeviceInfoToPlayFab(PlayFabApiSettings, IPlayFabInstanceApi) (at Assets/PlayFabSDK/Client/PlayFabDeviceUtil.cs:54)
PlayFab.Internal.PlayFabDeviceUtil:_OnPlayFabLogin(UserSettings, String, String, String, PlayFabApiSettings, IPlayFabInstanceApi) (at Assets/PlayFabSDK/Client/PlayFabDeviceUtil.cs:127)
PlayFab.Internal.PlayFabDeviceUtil:OnPlayFabLogin(PlayFabResultCommon, PlayFabApiSettings, IPlayFabInstanceApi) (at Assets/PlayFabSDK/Client/PlayFabDeviceUtil.cs:102)
PlayFab.Internal.PlayFabUnityHttp:OnResponse(String, CallRequestContainer) (at Assets/PlayFabSDK/Shared/Internal/PlayFabHttp/PlayFabUnityHttp.cs:234)
PlayFab.Internal.<Post>d__12:MoveNext() (at Assets/PlayFabSDK/Shared/Internal/PlayFabHttp/PlayFabUnityHttp.cs:198)
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr) (at /Users/bokken/buildslave/unity/build/Runtime/Export/Scripting/Coroutines.cs:17)

Don't mind the "/Users/bokken/..." paths, this is Unity's build machine, so no need to worry.

In our own implementations with UnityWebRequest we always use "using" blocks. This ensures that the request is always disposed of properly. I'm not sure why this isn't the case in PlayFabUnityHttp, but a first look seems to imply that it is indeed possible to create a memory leak when the manual call of

www.Dispose()

at the very end isn't reached... Interesting enough, the code contradicts @Ivan Cai's proposal of doing exactly this (using "using" blocks)...

Another error source seems to be in PlayFabEditorHttp:

A Native Collection has not been disposed, resulting in a memory leak. Allocated from:
Unity.Collections.NativeArray`1:.ctor(Byte[], Allocator) (at /Users/bokken/buildslave/unity/build/Runtime/Export/NativeArray/NativeArray.cs:69)
UnityEngine.Networking.UploadHandlerRaw:.ctor(Byte[]) (at /Users/bokken/buildslave/unity/build/Modules/UnityWebRequest/Public/UploadHandler/UploadHandler.bindings.cs:98)
PlayFab.PfEditor.PlayFabEditorHttp:MakeApiCall(String, String, GetStudiosRequest, Action`1, Action`1) (at Assets/PlayFabEditorExtensions/Editor/Scripts/PlayFabEditorSDK/PlayFabEditorHttp.cs:74)
PlayFab.PfEditor.PlayFabEditorApi:GetStudios(GetStudiosRequest, Action`1, Action`1) (at Assets/PlayFabEditorExtensions/Editor/Scripts/PlayFabEditorSDK/PlayFabEditorApi.cs:30)
PlayFab.PfEditor.PlayFabEditorDataService:RefreshStudiosList(Boolean) (at Assets/PlayFabEditorExtensions/Editor/Scripts/Utils/PlayFabEditorDataService.cs:198)
PlayFab.PfEditor.PlayFabEditor:OnEnable() (at Assets/PlayFabEditorExtensions/Editor/PlayFabEditor.cs:45)
PlayFab.PfEditor.PlayFabEditor:OnFocus() (at Assets/PlayFabEditorExtensions/Editor/PlayFabEditor.cs:62)
UnityEditor.HostView:RegisterSelectedPane(Boolean) (at /Users/bokken/buildslave/unity/build/Editor/Mono/HostView.cs:502)
UnityEditor.HostView:OnEnable() (at /Users/bokken/buildslave/unity/build/Editor/Mono/HostView.cs:154)
UnityEditor.DockArea:OnEnable() (at /Users/bokken/buildslave/unity/build/Editor/Mono/GUI/DockArea.cs:174)

In this case, at first glance, I can't find neither a using block nor any Dispose() call. Hope this helps...

Playfab SDK version: 2.107.210427(shown as latest release as of 2021-05-08)

Here's the stack trace that I did manage to then get - maybe this helps...

A Native Collection has not been disposed, resulting in a memory leak. Allocated from:
Unity.Collections.NativeArray`1:.ctor(Byte[], Allocator)
UnityEngine.Networking.UploadHandlerRaw:.ctor(Byte[])
PlayFab.Internal.<Post>d__12:MoveNext() (at Assets\PlayFabSDK\Shared\Internal\PlayFabHttp\PlayFabUnityHttp.cs:129)
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
UnityEngine.MonoBehaviour:StartCoroutineManaged2(IEnumerator)
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
PlayFab.Internal.PlayFabUnityHttp:MakeApiCall(Object) (at Assets\PlayFabSDK\Shared\Internal\PlayFabHttp\PlayFabUnityHttp.cs:119)
PlayFab.Internal.PlayFabHttp:_MakeApiCall(String, String, PlayFabRequestCommon, AuthType, Action`1, Action`1, Object, Dictionary`2, Boolean, PlayFabAuthenticationContext, PlayFabApiSettings, IPlayFabInstanceApi) (at Assets\PlayFabSDK\Shared\Internal\PlayFabHttp\PlayFabHTTP.cs:228)
PlayFab.Internal.PlayFabHttp:MakeApiCall(String, PlayFabRequestCommon, AuthType, Action`1, Action`1, Object, Dictionary`2, PlayFabAuthenticationContext, PlayFabApiSettings, IPlayFabInstanceApi) (at Assets\PlayFabSDK\Shared\Internal\PlayFabHttp\PlayFabHTTP.cs:133)
PlayFab.PlayFabEventsInstanceAPI:WriteEvents(WriteEventsRequest, Action`1, Action`1, Object, Dictionary`2) (at Assets\PlayFabSDK\Events\PlayFabEventsInstanceAPI.cs:63)
PlayFab.Public.ScreenTimeTracker:Send() (at Assets\PlayFabSDK\Entity\ScreenTimeTracker.cs:181)
PlayFab.Public.ScreenTimeTracker:OnApplicationFocus(Boolean) (at Assets\PlayFabSDK\Entity\ScreenTimeTracker.cs:156)
PlayFab.Internal.PlayFabHttp:OnApplicationFocus(Boolean) (at Assets\PlayFabSDK\Shared\Internal\PlayFabHttp\PlayFabHTTP.cs:332)
UnityEditorInternal.InternalEditorUtility:OnGameViewFocus(Boolean)
UnityEditor.PlayModeView:SetFocus(Boolean)
UnityEditor.GameView:OnLostFocus()
UnityEditor.HostView:OnLostFocus()