I have encountered a strange problem with Delta miles not being credited in the period of October and November of last year. I didn't have the problem before or after that period. And it's not even consistent across that time period.

During those two months, I had 22,000 miles not credited for paid flights flown on Delta (no codeshare or partner) in fare classes T, L and U. In some cases during that period, T, L, U were credited. In fact, there's one ticket where the outbound was credited and the return not.

I've not been able to get a response from Delta.

Thanks for any thoughts.