Evanix rex trigger sear failure

Have you contacted Evanix about this issue? That would be my first order of business.... actually you have already done the first order of business and don't shoot it.
I know you said you had it repaired but didn't say by whom?
If it was a gunsmith I would check and ask if he used locktight and get a letter from him explaining exactly what he did so you can forward it to Evanix.

My only other suggestion is to take it to an actual Gun Smith not an air gun store.
It was mentioned on the Kral thread that locktight doesn't stick well to oiled parts so it's possible that it is a simple matter of cleaning all the oil off then reapplying the locktight. Still when it comes to something that present such a danger I would suggest taking it to a pro just to make sure. ... A gunsmith may decide to retap the threads for a tighter fitting screw.

Sorry I can't be more help Neils I'm actually wondering if the plate that screw goes through has enough "meat" on it to keep the screw from wallowing out and backing out.
My only other possible right now fix would be to set the trigger up( adjust it) then take some thick epoxy mix up very small amount the take a toothpick and put a dot on the screw/plate to lock it in, don't put it on the threads just use it on the head and plate to keep the screw from turning out
You might even be able to do the same with fingernail polish. You might need to take and lightly sand the screwhead and plate to give the epoxy or polish something to bite to, again just make sure you don't get it on the threads your just trying to bridge the head of the screw and the plate with the epoxy or polish so it locks the screw and it can be broke away fairly easy without any harm