Mini List collapsed by itself midway through a Solo Mythic Antorus run. Ctrl + Click doesn't expand it. All other commands work perfectly. Main list works 100%.

Closed and re-opened the game several times, reinstalled ATT both manually and through CurseForge, deleted all settings and preferences and opened the game with ATT being the only add-on loaded. Not entirely sure what else I can do to troubleshoot.

What do you mean collapsed? All headers are collapsed (like Quests, Vendors, etc)? Can you show a screenshot?

To reset the ATT windows to the default onscreen size run:
/script AllTheThings:GetWindow("CurrentInstance"):SetSize(400,400);