After going through old TDMModel service logs, I noticed few errors related to Java heap space.
These errors are during saving the model file.
To resolve this heap space issue, please increase the memory used by TDM portal by making changes in wrapper.conf file (C:\Program Files\CA\CA Test Data Manager Portal\service\conf\wrapper.conf).
Steps to increase memory for TDM is available at below article:
After making the changes, restart the portal service and verify the issue.
java.lang.OutOfMemoryError: Java heap space
Wrapped by: com.sun.xml.messaging.saaj.SOAPExceptionImpl: Error during saving a multipart message
... 47 common frames omitted
Wrapped by: org.springframework.ws.soap.saaj.SaajSoapMessageException: Could not write message to OutputStream: Error during saving a multipart message; nested exception is com.sun.xml.messaging.saaj.SOAPExceptionImpl: Error during saving a multipart message