Citi shut down my Double Cash card last month, which I have been using for both MS and organic spend for 5+ years. The initial letter provided no reason for shutdown, said I had to write them a letter & ask for explanation, which I did. Their response:
"Based on a review of your account, we observed account activity that is inconsistent with typical consumer usage and payments for which the source of funds could not be determined."
FWIW, I made intra-monthly payments using both WM BP and Citi's own payment button (linked to my checking account). However, I always had sufficient CL headroom for my spending, regardless of the intra-month pay downs.
To add injury to insult, they also "declined" to pay out my accumulated cash rewards (about $150), citing the terms of the program.
I have plenty of other dogs in the hunt, so not really too upset except for the lost cash. I resolve to be more diligent about cashing-out.