I am not really able to share my project too much, so I will have to skip on your offer.
However, from what I have seen yesterday, it seems like after these problematic long level loads, tracking origin is not being set to “Floor level”. Forcing it to this value fixes the wrong camera offset but it does not fix unbelievably long loading times (which are the bigger problem).
So it is likely not caused by a mistake in, let’s say my code. I have no idea what to do for now other than “dropping” support for Rift temporarily and counting on 4.19 to resolve the issues.