In the METUP Project: [https://unity3d.atlassian.net/browse/METUP-196]

See *IN-64594* for complete repro project.

Running a basic sample like SimpleAR, planes will show up for 10-20 seconds before being “removed”.

Repro:
# clone arfoundation-samples 5.1 [GitHub - Unity-Technologies/arfoundation-samples at 5.1|https://github.com/Unity-Technologies/arfoundation-samples/tree/5.1]
# add com.unity.xr.meta-openxr@1.0.1 to the project
# configure XR Plug-in Management to use Meta Quest
# run Space Setup on Quest 3
# run the SimpleAR sample
# observe that planes appear initially, but are removed after 10-20 seconds.

Andy Biar thought maybe it had to do with the planeAlignmentThreshold, but setting it to a large value (1000) had no effect. Relevant logs from my test:
{code:java}
2023/12/28 13:16:22.971 8145 8165 Info Unity [tmow] planeAlignmentThreshold=10002023/12/28 13:16:27.972 8145 8165 Info Unity [tmow] planeAlignmentThreshold=0.005
2023/12/28 13:16:32.973 8145 8165 Info Unity [tmow] planeAlignmentThreshold=1000
2023/12/28 13:16:37.986 8145 8165 Info Unity [tmow] planeAlignmentThreshold=0.005
2023/12/28 13:16:42.987 8145 8165 Info Unity [tmow] planeAlignmentThreshold=1000
2023/12/28 13:16:47.999 8145 8165 Info Unity [tmow] planeAlignmentThreshold=0.005
2023/12/28 13:16:50.777 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane C9A89C302547F6D3-88FBEEC606654D23" alignment=HorizontalUp normal=(0.00, 1.00, 0.00)
2023/12/28 13:16:50.778 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 0AE76CE70CA006AC-44FE941A9C7FCBBF" alignment=HorizontalUp normal=(0.00, 1.00, 0.00)
2023/12/28 13:16:50.779 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 757FC1A6888829F1-07EC9C69C2B2243C" alignment=HorizontalUp normal=(0.00, 1.00, 0.00)
2023/12/28 13:16:50.780 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 44048C79C98D6A1C-F58D92DB244F3018" alignment=HorizontalDown normal=(0.00, -1.00, 0.00)
2023/12/28 13:16:50.781 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 3D3CA6E10B2AB9FF-311E561A94B7D48C" alignment=HorizontalUp normal=(0.00, 1.00, 0.00)
2023/12/28 13:16:50.782 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane A6F60C1CAA5F8AD1-C7A9A8126D6D3C08" alignment=Vertical normal=(0.69, 0.00, -0.72)
2023/12/28 13:16:50.782 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 936F97A74ECF3E82-7CF9D51FABA6BEDE" alignment=HorizontalUp normal=(0.00, 1.00, 0.00)
2023/12/28 13:16:50.783 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 045C44D3AEAB1A53-628A9BF5D2ABA7BD" alignment=Vertical normal=(-0.57, 0.00, -0.82)
2023/12/28 13:16:50.784 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 9E88FB6EAA688D7A-8C1DC75E7019F81B" alignment=HorizontalUp normal=(0.00, 1.00, 0.00)
2023/12/28 13:16:50.785 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 0BB5C880925891D7-E52684F964209C11" alignment=HorizontalUp normal=(0.00, 1.00, 0.00)
2023/12/28 13:16:50.786 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane A376CD66FA7FF43F-95225B7BCAFE97AD" alignment=HorizontalUp normal=(0.00, 1.00, 0.00)
2023/12/28 13:16:50.788 8145 8165 Info Unity [tmow] [Plane Removed] name="ARPlane 23A639C9A53347F0-9A39AF0C30A90192" alignment=Vertical normal=(-0.18, 0.00, 0.98){code}
Note that every 5 seconds I toggle the planeAlignmentThreshold between 0.005 and 1000. There is no apparent effect. After about 30 seconds, the ARPlaneManager removes all planes.

Note this is also reproducible in the Mixed Reality Template