We worked around this for a little while by just commenting out the plugin when building the bootwar, and only enabling it when we were doing migrations.

How would you deploy the migrations if it didn’t work in the standalone tomcat?

We run the migrations from a separate workstation, not from the server instance, using grails dbm-update. (Well, dbm-status, then dbm-update.) We don't, for example, use the dbCreate: update option for the data source.

Thanks for the info! I might be able to mange that until we can get to Java 11 and newer version of grails

A similar workaround did the trick for us; the only difference I see is that we’re using a newer plugin (the one shown is 4.1.0); not sure if that’s why ours is working, but it might be worth trying:

implementation ('org.grails.plugins:database-migration:4.2.1') { exclude module: 'spring-boot-cli' }