Unfortunately the upgrade to Unity 6 resulted in some old solutions no longer solving correctly. Although we tested old solutions as part of the engine upgrade, we didn't catch some cases that our users have reported.
It's more important for us to keep previous solutions working for our players than to upgrade the underlying engine (which was a nice-to-have, not a necessity). So we have rolled back to the older version of Unity, while still keeping the other improvements and fixes from 1.5.16.
Sorry for any inconvenience, and thank you to our players for reporting this problem!