Not a direct reply to Larbot but has anyone had the issue of shifting from the small chainring to the large chainring and the chain falls IN getting stuck between the frame and the small chainring?

I'm out of ideas. I've had two trusted bike mechanics look at it and it's got all of us? It's the stock ROTOR and rings. Happens so sporadically that it's hard to understand what is unique that makes it happen.

Things like chainring orientation, derailure alignment, chain orientation have all been checked and rechecked. Chain is not worn. Has happened on every chain the bike has had. SRAM KMC doesn't matter.

I've added a chain catch which has helped but it happened today where the chain didn't fall behind the catch but got off the small chainring on the bottom side (but not stuck in between frame and brake like it has in the past) while the top was something odd between the catch and the small ring while the derailure was over the large chainring. Rear cog was in the middle so no extreme cross chaining.

Pulled it out and immediately started shifting from small to big trying to make it happen again. Nope. All good. I was shifting from warming up to starting to pedal. Wasn't under tension. Was a smooth pull of the shifter lever. I don't know how/what/why it happened.

Shifts super smooth all other times except for when it does this.

I live in Florida so I don't have to worry too much but have IMLP coming up and I'd prefer to not be coming down and have my chainring lock up my pedals and crash.

I hope someone points out something obvious and I feel dumb but get it fixed. Thanks.