Cannot activate one ritual altar

Bug id 1,315,234,302

I could initiate three rituals, but one never activated, and I couldn't start it.
I had 0 monsters remaining, so I definitely didn't miss one.
I've done plenty of maps with ritual altars in the last few days, this is the first time one couldn't be initiated.

this happened again
Bug Report ID: #2,808,666,838

This happens with 2 times already