Do the tatoos have their own equipment slot, are they a body skin or something else? The catsuit gets the standard path for the body skin texture so there might be an incompatibility there if you have something that maybe makes your character grab a different skin file.
No, regular RaceMenu and SlaveTats overlays.
Fixed the underbreast issue, I clearly remember fixing the left underbreast but I must have messed up by forgetting to turn the mirror option back on so it didn't apply to the right underbreast. I'll upload this after I figure out this tattoo business.
I've previously been curious about it so I've installed the SlaveTats mod, after applying a few tattos I didn't have a problem, could you point me to the tattoo pack and the specific tattoos you're using? I wanna figure this out.
I made a quick test and the vanishing tattoos bug happens with the following:
Black - OK
Black (new boots) - no tattoo
Black (no boots) - no tattoo
Black 2 - OK
Black 2 (new boots) - no tattoo
Black 2 (no boots) - no tattoo
Red - OK
Red (new boots) - no tattoo
Red (no boots) - no tattoo
Red 2 - OK
Red 2 (new boots) - no tattoo
Red 2 (no boots) - no tattoo
Here are some test shots using RM overlays from here and SlaveTats overlays from here.