I’m running with other mods with “no monsters” on v1.14.5 (stable) with no problems. Have you tried with only “no monsters” enabled?
I suggest that some other mod is causing the crash when “no monsters” is enabled. I say this because “no monsters” is simply a patch that disables locusts and drifters. It doesn’t have any code that could possibly crash.
If some other mod depends on those entities being enabled, that other mod may crash. You might determine which other mod that is by enabling only "no monsters", verifying that it causes no crash by itself, then enabling (one-by-one) the other mods and checking for crash.
I'm interested in which mod is having issues when "no monsters" is enabled.