Maybe it's because some mods don't go well together: K2 has its own armors and vehicles, and its not for defense against stronger biters but it's only for fun and fresh play, while RA is made specially to survive in Rampant world with New Enemies set as ON. RA isn't good without Rampant and New Enemies.
Try to mix mods of different usage to avoid surprises and problems. Unfortunately there are not many such mods specializing in something - expanding nature objects, adding weapons&armours only, adding trains managers, adding special vehicles (for example this mod conflicts even with AirCraft mod because of two Napalm ammo variants), adding monsters (the last one is tricky, because requires special counter-biters mod - like written above or like Bob's Enemies requiring Bob's warfare mod to have a balance in turrets range and damage type VS monsters range and damage resistances)
To be honest K2 conflicts with almost everything except some very small specialized mods. The only big mod exception is probably Space Exploration.
Also K2 doesn't add biters challenge in the game, so there is no use for RA there. K2 already has overpowered weapons and military technology trees.
