After playing with `adb logcat` filters I did find some errors; given that I didn't modify anything in the MirrorScene I'm not sure why things would not be fully set up so these may be normal, and there don't seem to be any further errors after the 'user avatar successfully loaded' message that gets logged after these -- but maybe someone has seen something similar?
2022/01/12 01:01:03.571 29406 29430 Error Unity [ovrAvatar2] Can't access joint Head unless it is in critical joint set
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.Logger:Log(LogType, Object, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.Debug:LogError(Object, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:Log(ELogLevel, String, String, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:LogError(String, String, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity SampleAvatarEntity:GetSkeletonTransform(ovrAvatar2JointType)
2022/01/12 01:01:03.571 29406 29430 Error Unity SampleAvatarGazeTargets:CreateGazeTarget(String, ovrAvatar2JointType, ovrAvatar2GazeTargetType)
2022/01/12 01:01:03.571 29406 29430 Error Unity <Start>d__4:MoveNext()
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
2022/01/12 01:01:03.571 29406 29430 Error Unity
2022/01/12 01:01:03.571 29406 29430 Error Unity [ovrAvatar2] SampleAvatarGazeTargets: No joint transform found for HeadGazeTarget
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.Logger:Log(LogType, Object, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.Debug:LogError(Object, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:Log(ELogLevel, String, String, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:LogError(String, String, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity SampleAvatarGazeTargets:CreateGazeTarget(String, ovrAvatar2JointType, ovrAvatar2GazeTargetType)
2022/01/12 01:01:03.571 29406 29430 Error Unity <Start>d__4:MoveNext()
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
2022/01/12 01:01:03.571 29406 29430 Error Unity
2022/01/12 01:01:03.571 29406 29430 Error Unity [ovrAvatar2] Can't access joint LeftHandIndexProximal unless it is in critical joint set
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.Logger:Log(LogType, Object, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.Debug:LogError(Object, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:Log(ELogLevel, String, String, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:LogError(String, String, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity SampleAvatarEntity:GetSkeletonTransform(ovrAvatar2JointType)
2022/01/12 01:01:03.571 29406 29430 Error Unity SampleAvatarGazeTargets:CreateGazeTarget(String, ovrAvatar2JointType, ovrAvatar2GazeTargetType)
2022/01/12 01:01:03.571 29406 29430 Error Unity <Start>d__4:MoveNext()
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
2022/01/12 01:01:03.571 29406 29430 Error Unity
2022/01/12 01:01:03.571 29406 29430 Error Unity [ovrAvatar2] SampleAvatarGazeTargets: No joint transform found for LeftHandGazeTarget
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.Logger:Log(LogType, Object, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.Debug:LogError(Object, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:Log(ELogLevel, String, String, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:LogError(String, String, Object)
2022/01/12 01:01:03.571 29406 29430 Error Unity SampleAvatarGazeTargets:CreateGazeTarget(String, ovrAvatar2JointType, ovrAvatar2GazeTargetType)
2022/01/12 01:01:03.571 29406 29430 Error Unity <Start>d__4:MoveNext()
2022/01/12 01:01:03.571 29406 29430 Error Unity UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
2022/01/12 01:01:03.571 29406 29430 Error Unity
2022/01/12 01:01:03.572 29406 29430 Error Unity [ovrAvatar2] Can't access joint RightHandIndexProximal unless it is in critical joint set
2022/01/12 01:01:03.572 29406 29430 Error Unity UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
2022/01/12 01:01:03.572 29406 29430 Error Unity UnityEngine.Logger:Log(LogType, Object, Object)
2022/01/12 01:01:03.572 29406 29430 Error Unity UnityEngine.Debug:LogError(Object, Object)
2022/01/12 01:01:03.572 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:Log(ELogLevel, String, String, Object)
2022/01/12 01:01:03.572 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:LogError(String, String, Object)
2022/01/12 01:01:03.572 29406 29430 Error Unity SampleAvatarEntity:GetSkeletonTransform(ovrAvatar2JointType)
2022/01/12 01:01:03.572 29406 29430 Error Unity SampleAvatarGazeTargets:CreateGazeTarget(String, ovrAvatar2JointType, ovrAvatar2GazeTargetType)
2022/01/12 01:01:03.572 29406 29430 Error Unity <Start>d__4:MoveNext()
2022/01/12 01:01:03.572 29406 29430 Error Unity UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)
2022/01/12 01:01:03.572 29406 29430 Error Unity
2022/01/12 01:01:03.572 29406 29430 Error Unity [ovrAvatar2] SampleAvatarGazeTargets: No joint transform found for RightHandGazeTarget
2022/01/12 01:01:03.572 29406 29430 Error Unity UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
2022/01/12 01:01:03.572 29406 29430 Error Unity UnityEngine.Logger:Log(LogType, Object, Object)
2022/01/12 01:01:03.572 29406 29430 Error Unity UnityEngine.Debug:LogError(Object, Object)
2022/01/12 01:01:03.572 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:Log(ELogLevel, String, String, Object)
2022/01/12 01:01:03.572 29406 29430 Error Unity Oculus.Avatar2.OvrAvatarLog:LogError(String, String, Object)
2022/01/12 01:01:03.572 29406 29430 Error Unity SampleAvatarGazeTargets:CreateGazeTarget(String, ovrAvatar2JointType, ovrAvatar2GazeTargetType)
2022/01/12 01:01:03.572 29406 29430 Error Unity <Start>d__4:MoveNext()
2022/01/12 01:01:03.572 29406 29430 Error Unity UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)