Please see the application server logs as well which will provide more information if something not available in cmxserver logs. So please share application sever log errors for investigation.
Please share complete stack trace from cmxserver and application server logs to get more idea.
Are you using sql server Database, There is a similar known issue MDM-13372 and is documented in Release notes. Please check if ActiveVOS URL and workflows are working, if so you can ignore this error.