Dragonwheel I know what this is. To fix it, temporarily move your save to an earlier build, complete this section, save, move it back.
Changes were made in two places recently:
- Hidden Stronghold
- Yhilini Order of Thaumaturgy
To lock the party to prevent Simon from using Command to swap people when he wasn't supposed to be able to do so for plot reasons. It looks like that fix did not work as intended. I'll pass this along.