I had this problem with one of my XPA-1L amps and I finally had to pop the cover off and play with the trigger jack connection.
This fixed the problem.
You might try to see if you can clean the inside of the connection somehow with a little isopropyl alcohol.
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Epson 3500 3D projector
93" Carl's Place Flexiwhite DIY screen
Outlaw 976 Pre/Pro
Outlaw 7500 for center and surrounds
2- Emotiva XPA-1Ls for LF/RF duty
2- Outlaw LFM-1 EX subs
Oppo BDP-105 Blu-ray/DVD/SACD player
Outlaw LCR (Snell Labs) for center channel duty
Tekton Lore monitors L/R
4- Emotiva ERD-1s surround speakers
Monster HTS3600MKII power center