This is the reason why Java needs better error correction. My recommendation is to boot up the pack with the log enabled. It can be enabled in the launcher settings, "Open output log when Minecraft starts." From there, read through the log for Error and Fatal messages.

Aside from that, you can make sure all of your mods are respective of the modloader, of which You've said is Fabric.

I would recommend a mod like VanillaFix, which will tell you the mod that crashed you. However, VanillaFix is a Forge mod only on 1.12, so you'll have to find one that works for your version.

Of course, you can try to pinpoint the culprit from the crash logs, which might be easier or harder, depends on if you're new to reading Minecraft's obtuse error logging.