This is a common problem on mkI units afaik. I don’t know why it happens or how to fix it, I had mine repaired under warranty (repair report said something like “resoldered all audio connections”) but later on the problem came back.
I’ve not had this issue with the OT MK1 but my headphones in general are to blame, the left signal cuts out and the connection on the right needs a wobble. The Sennheiser HD25 is a cruel mistress.
If it’s like what happened to me and others, you can get the sound back by blasting something really loud, i.e. put a compressor on a track and turn the makeup gain to max. Might want to lower you headphone volume during this.
I had a power socket problem, repaired by bending the part of metal in it, with a little flat screwdriver. The metal part was too loose to make good connection with the power supply. MKI.