Few years back I replaced the trigger with an Apex to cure the gritty feel, been working fine.

At the range today, fired a mag then trigger froze, wouldn't budge. I removed the ammo. I depressed only the trigger safety with one finger, then press the trigger with another finger and it clicked. But the trigger would lockup firing with my trigger finger.

This happened live firing with the Mantisx shield base plate for the Mantisx firearms training system: https://mantisx.com/ I replaced the shield base with their bluetooth adapter so it would communicate with my IPhone or my Kindle. I don't believe that caused the trigger failure because I dried fire for two weeks straight.

When I take the trigger assembly out, what should I look for?