Hundreds of CMJ Integrity Check violations prevent snapshot from being created.
There is no ultimate solution, but there is a number of guidelines that will eventually lead to a successful snapshot creation.
Make sure that the latest version of CMJ is used, as it's constantly improved, IC included
Run a Full Integrity Check on this system with filters, Agile boards and dashboards included https://botronsoft.atlassian.net/wiki/spaces/CMJ/pages/8257541/Integrity+Check
Only violations with severity "Error" will prevent snapshot creation and need to be fixed, because such violations mean that this is invalid configuration, that cannot be deployed on your destination instance (usually the underlying Jira API that CMJ uses does not allow it)
Start with any "Unknown" errors - these are very exceptional cases that usually signal an unusual misconfiguration of Jira
After there are no more "Unknown" errors, proceed with the "known" ones - use Quick fix when there's one available https://botronsoft.atlassian.net/wiki/spaces/CMJ/pages/517799941/Quick+Fix Common errors are related to Agile boards/filters referencing missing objects - the groovy scripts listed here can be useful https://kb.botronsoft.com/pages/viewpage.action?pageId=6586481
For the remaining errors, use the suggested resolution in the IC violation UI https://botronsoft.atlassian.net/wiki/spaces/CMJ/pages/8257541/Integrity+Check to either fix via Jira's UI or through a custom groovy/SQL script