Downloaded the xr foundation samples today, and noticed that the preview package 3.1 is missing from the package manager. What’s strange is that I just downloaded them last week and the package was there, now the highest it goes is 3.0. 3.0 is incompatible with some of the API calls that the samples make.
Furthermore, I tried copying the package cache and the manifest from a found version, with Unity just removing them upon launch.