Camera texture stops updating but tracking continues

Hi

I'm (cross)posting this here because I've had to create a dual solution due to Groundplane not yet supporting ARCore. For iOS I'm using Groundplane, but for Android I've had to use ARCore. It's my feeling that the ARCore is malfunctioning due to the erroneous startup behaviour of VuforiaBehaviour. I can't be sure though as I'm not seeing an errors in the log - just visual errors.

I have an issue using Unity 2017.3.1p3 where the camera texture can sometimes stop updating - ie it freezes - and yet tracking still continues, so then the screen is no longer being cleared(as the Unity camera is Depth only clear) , which is obviously results in a bit of a mess.

ARCore has to coexist with Vuforia in the same Unity project. Could this make a difference? VuforiaBehaviour component attaches to your camera automatically - even though ARCore is enabled, and Vuforia is disabled. Grrrr. Ugly code gymnastics are required to turn it off, but in that single frame where it was enabled, who knows if that would have caused issues for ARCore? I don't know if this is the cause - I'm just mentioning it as a possibility. Vuforia also has delayed initialisation enabled so in theory it shouldn't interfere (more than being an annoyance).

What I can say is that it happens more frequently on the "older" phones like Google Pixel and Samsung S8. On Pixel 2 it's extremely rare.

Given the black box nature of Unity all I can do is to trial and error change things around - but I've never been able to get rid of the issue.

Has anyone else had this experience?

Thanks
Scott

ARCore 1.1
Unity 2017.3.1p3 (Vuforia version 7.0.47)