Sounds like the latch is just sticking. your best bet is to remove the trigger assembly, and completely disasemble the gun, clean it out the nside concentrating on the internally mounted items and then clean the trigger assembly really good. Blow it all out with compressed air (or those cans of air for cleaning a computer work great too) then lightly (VERY LIGHTLY) oil the moving parts where they touch. also oil the rails that the bolt sliede in.
It could just be old oil or dirt holding it up.
CPL holder since 1991, NRA Lifetime Member, DU Member, NICET certified
"For those who would give up essential liberty to purchase a little temporary safety, deserve neither Liberty nor safety.—Ben Franklin.”