To follow up my own post, the mystery AM station cut off suddenly at 2338 UTC and then the DRM signal came in at good strength again. Looks like someone noticed what was happening and corrected the situation.
Modified NRD-525G with Radiokit DRM Decoder Board,
SDRplay RSP-1A, Airspy HF+ Discovery, Dream v2.1.1
Lancashire, UK 53:39.18N 02:10.28W IO83vp