Please share screen shots for your Authentication Service.
You can try tracing through SAML tracer. You can also enabled below loggers, after that you will get more information in logs which will help you to debug the issue. You can check pega-rules logs after that. If you don't find the issue yourself, share the logs and SAML tracer results here with us.
Also try to re-import IDP metadata once and check.
To enable logger as mentioned in above comment you can follow below path:
Dev Studio-> Configure -> System --> Operations --> Logs --> Logging Level Setting --> Provide Logger name one by one --> Set Current Level to Debug