So I was under the understanding that this mod was server side, so I included on my fabric server. unfortunately there seems to be issue where if they try to break spawners (the ones under the tombs), their games crash. also, there are random crashes that seem to happen randomly if someone is in the stronghold.
crash report.txt
The issues seem to be fixed by removing the mod, given its generated everything, but now theres console spam of the line:
[11:22:10] [Server thread/ERROR]: Unknown structure start: betterstrongholds:stronghold
Is this fixable?

Closing due to inactivity.

I don't think this is caused by Better Strongholds, considering these problems happened when the strongholds were already generated. If Better Strongholds were to cause problems, it would happen during generation, since that's all the mod does. It doesn't touch anything after initial world gen. Unfortunately I can't help you much just from that crash report alone.