Reproduction steps:
1. Open the attached project "PlanarReflectionProbe1.zip"
2. Open "SampleScene.unity" under "Assets/Scenes" folder
3. Enter Play Mode

Expected result: Planar Reflection Probe continues to reflect the background during the animation and after
Actual result: Planar Reflection Probe stops reflecting the background during the animation and after

Reproduces on: HDRP 5.7.2-preview (2019.1.2f1, 2019.1.14f1), HDRP 7.2.1 (2019.3.3f1, 2020.1.0a25)
Could not test on 2017 due to HDRP not existing
Could not test on 2018.4 due to imported reflective shader throwing exceptions in the Console window
Could not test on 2019.1.1f1 and below due to the HDRP Scene completely breaking and/or exceptions being thrown related to Planar Reflection probe

Notes:
-Changing the Planar Reflection Probe Clipping Planes "Far" property in the Inspector window solves the issue
-Planar Reflection Probe stops reflecting the background when the animation finishes playing