The dimension arsomega:demon_realm is missing a dimension type. This leads to several issues, including but not limited to:

• Breaking the /forge dimensions command
• Causing chunkloading problems with Immersive Portals

Same issue on 1.18.2

1.18.2 is no longer supported at this point because keeping up with 1.19 is hard enough. Unless anyone has issues in 1.19 (or a future version) I'm gonna close this as I've only heard issues from 1.18

mod version?

I've the same problem

Minecraft: 1.18.2
Ars Omega: 2.7.4
Forge: 40.2.10

two questions:
were you on a superflat world?
can you see if relogging fixes the issue?

The worldtype does not seem to influence the issue in any way. Relogging does not fix the issue.