After several hours of testing today, it appears that Forge version 1.6-179 of quark for Minecraft version 1.12.2 will not generate stalagmites or stalactites in caves when Yung's Better caves version 1.12.2-2.0.4 or Realistic terrain generation version 1.12.2-6.1.0.0-snapshot.1 or Realistic Terrain Generation Unofficial (development fork of the former) version 1.12.2-1.1.0 are also installed on the same instance of Minecraft. I have already made several test worlds in version 1.12.2 of minecraft with varying combinations of the above mods present with version 1.6-179 of quark and stalagmites/stalactites are always absent from cave generation. I have included the Minecraft log for one case where I generate a world with RTG version 1.12.2-6.1.0.0-snapshot.1 and Yung's Better Caves version1.12.2-2.0.4 present, but let me know if you need other logs where I generate worlds with more combinations of the offending mods present.

Because this is more of an issue of mod compatibility than a problem with the mod itself, it might be lower priority than an actual bug causing Minecraft to crash.
Log_For_RTG.txt

I edited the cfg file for a bit this evening to see if the generation conflict with RTG and Yung's better caves was merely reducing the rate at which stalagmites and stalactites are spawning and it seems that increasing the percentage chance at which these items generate has no noticeable effect even as high as 10.0 percent for stalactites.

I went through the trouble of skimming through the log text file and it appears that during the spawn generation period, the log mentions something called "cascading worldgen lag." I'm uncertain that this means or if it's of any help in finding out why stalagmites and stalactites don't generate properly.