Internal Server Error on REST API invocation

Hello Everyone,

In recent days, We are seeing this error in the tomcat-stdOut.log. In the front end, we are getting, An error encountered while processing the request.

ERROR com.appiancorp.rest.shared.FallbackExceptionMapper - Internal Server Error on REST API invocation. com.appian.komodo.api.exceptions.SignalException: At least one referenced Activity Class Schema is invalid: ,304

Can you help us on solving this issue?

Thanks in Advance