By "still soap suds in the machine", do you also mean the rinse water (with suds) is still present? In which case possibly the drain pump has a sock or underwire blocking the impellers?

EDIT: seems unlikely given the sequence you have observed, but still worth a check. Otherwise I might guess that perhaps the machine simply needs a cleaning (soap gunk builds up over time, and some washers have a special cleaning cycle and solvent to accompany that).