I'm having a sporadic drain problem. At the end of the washing cycle, there is either a pool of soapy water, less soapy water, or dry but a lot of residual suds. Also occasionally it oversuds and suds leak out. All can usually be rectified by a single rinse cycle.

From what I infer, the dishwasher is missing one (or more) of the drain cycles. The varying symptoms resulting from which drain cycle is skipped.
The drain is working, as evidenced by the fact that I can just put it back through the rinse and it works normally.

Any ideas how to diagnose and fix this issue?
Thanks,
Tom