Custom weapons needs unique names otherwise there is a conflict between mods. Even by the same author.
I had to rename my Seacats for the
60's Hermes (Seacat_69),
70's/80's Hermes (Seacat_H - same folder/mod so it is okey)
and my patrol boats (Seacat_V).
DCS is delicate and confused when things are named the same in different folders.