Ritual encounter in Pit map boss fight can be uncompleteable

https://imgur.com/a/9PGCs6X

I just completed a Pit map where I had 4 ritual altars. I cleared the first 3 with no problem but the 4th one which was in the boss room was uncompleteable.

I entered the boss room, the gates closed, and I started fighting the boss and the mobs but before I finished and the gates opened I started a ritual encounter which was there. The ritual did not cover the whole arena so there were mobs that were not part of the ritual and were still alive so the arena gates remained closed through the whole encounter. The problem is that the ritual ring was reaching a little outside one of the gates and spawned a few ritual monsters there. I couldn't reach these monsters because the gates were closed because there were normal map arena monsters still alive outside the ritual and I couldn't kill them either because I was in a ritual encounter. The only thing I could do was to portal out and fail the encounter.