Hi dlgregory and welcome to the Mattermost forums!
You cannot directly upgrade from 5.27 to 7.4.0, you need to upgrade to the latest 5.x release first. If you do not do that, you will have some database migrations missing which could cause the problems you’re seeing here.
What database server in what version with what collation on the databases/tables are you running on the 5.27 deployment under OpenBSD?