Started this game a few months back and am enjoying it so far

One thing that does mystify me and I've found no solution for yet is....

I synthed up a guardians relic on one of my 5 and equipped it and it looked fine but when i went back later it was gone. Found it in the blacksmiths list of stuff i can work on but not allocated to any.

PLEASE help me get it back on my formation !!!! I had it enchanted to lvl 21 and it sucks to not be able to use it.