Help needed - Only one channel playing!

I am stumped and hope someone can help solve this mystery.

My left AGD Audion mono block stopped playing, while the right one was ok. They are connected directly to a Denafrips Terminator Plus XLR output, but the RCA output also did not fix the problem. I then moved the right amp to the left side after verifying that the cables and connections were okay (even though they had not been touched before the problem). The right amp that had been playing now did not play with the left connection. Alberto (AGD) checked the amps and verified they were testing normally.

Eventually, after many days and playing two different integrated amps, which played both channels, I reconnected the Audions both channels played as expected. Now the problem has returned BUT on the right channel. I moved the right amp to the left channel and verified it plays normally. In other words, the problem has returned, but now the other (right) channel is dead, but only with the Audions, bc I reconnected an integrated, and both channels play as expected.

All connections seem ok, and the problem occurs whether there is an XLR or RCA output connection.

I power reset the TPlus and hard reset the Lumin U2, but that did not help.

I think the problem is in the TPlus, but it's just a guess through the process of elimination.

If anyone has suggestions for correcting this problem, I would appreciate it if you could respond to this message. I'm out of ideas.

Thank you

Michael