As far as general references go, I think your best bet is to attend a HEC-RAS class since they will supply you with materials that talk about common troubleshooting for model stability. In addition to that, you get one-on-one time with the developers. So to answer your question, there’s a “Troubleshooting with HEC-RAS” section in the HEC-RAS Users Manual, but outside of that, I doubt there’s a quick reference guide to troubleshooting general issues.