I had a tribe of nudist colonists when a yearly skylantern festival was due. However, it was very hot outside when I started it. The colonists moved to the wood in storage, then remained there, standing and socializing at the wood and not the ritual spot (and certainly not building any lanterns).
Upon experimentation, it seems that a temperature of over 36 C is enough to prevent them from heading outside. (I haven't tested if it happens at especially low temperatures, nor if wearing appropriate clothing changes the threshold.) Eventually the festival "ends" and is cancelled due to lack of attendance.
In the log, there were repeated instances of
TryMakePreToilReservations() returned false for a non-queued job right after StartJob(). This should have been checked before. curJob=PrepareSkylantern (Job_701)
(Filename: C:\buildslave\unity\build\Runtime/Export/Debug/Debug.bindings.h Line: 39)
for various job numbers as they stood around.
Either the festival should be unstartable in dangerous temperatures or they should be able to party through the sweat.
I have rigged up a save file that exhibits the problem. Load it and start a festival to see.
Thanks for the bug report, I was able to reproduce this this issue on your provided save. I can see the issue and I'll write in a report that will suggest either rituals can't take place in extreme temperatures, or the player is warned and it continues during extreme temperature.