After a good nap I have to correct myself. It should be happening on both the snap package and deb package, it worked on the repository deb package(version 3.0.3) because forkproxy had changes since 3.0.3 which added epoll calls.
After looking into the problem, This issue is happening on LXD 3.11 with both(snap + deb/compiled)
Somewhere between the epoll_ctl call and the epoll_wait call it appears to be returning the wrong value, I haven’t had time to look further into this however.