Op-1 issue with left side keys

Hello, I’m having the intermittent issue with left side keys not working (everything on the left of the C note) and I’ve knew about some different ribbon cable.
The thing is once I turn on and press some keys for some time it start working OK.
But after sometime with op-1 on the keys stop working again.
Any ideas if it is a physical problem (ribbon cable) or electrical one? I would love to fix it myself.