Did my Tonedexter kill my AG Stomp?

[shufflebeat]

This is a story of a delayed "A-Ha!" moment, maybe. For the actual question look under the ------ line.

I used to use a Yamaha AG Stomp (fave pedal #1) until I went all Tonedexter (fave pedal #2). At one point I decided they should join forces rather than compete for my affections (effections?) so I put the AG in the FX loop of the TD with a regular insert lead.

All seemed well despite an apparent level mismatch which required me to run the AG at full throttle to keep up with the expectations of the TD FX return. After a few promising tries the AG went a bit quiet and stopped doing anything out of the L(mono) output. The AG got retired and put in a nice box marked, "get this fixed".

So, fast forward a couple of years and I open the box and feel a pang of guilt for not having the AG repaired. For the first time I'm imagining the processes that might have led to the problem. Here's the issue:

The AG has two outputs, L&R, both are balanced on TRS jacks. The L is marked "mono" but I don't actually know if it is or it's just marked that way, otherwise muppets like me will hassle music tech fora asking, "which output...?". It may be that L is just one side of the reverb/chorus (which might cancel out if summed).
-------------------
I used a balanced TRS in the FX loop of the TD and needed to use maximum level for it to be heard, did I bridge a balanced output and would this fry an op-amp?

[resistorman]

Have you tried it on its own to see if it actually is broken recently?