ARTrackedImageManager has strange performance issue

Unity Engine
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1

We try to use ARTrackedImageManager to perform 2D image tracking.
When it works once(trackedImagesChanged calls once, ARTrackedImagesChangedEventArgs.added list has value) and the app keeps running about 10 minutes without doing other operations, the performance becomes unstable.
If the app continues running, FPS will go down to under 30.

Here is our test environment:
Unity: 2020.2.1f1
ARFoundation/ARKit: 4.1.7
iPhone X

Is this the ARFoundation bug?
Is there any trick to avoid this issue?

2

Please kick us a bug report: Unity QA: Building quality with passion