Sites crashing on admin login after update

I am experiencing a very odd issue that seems to be related to the recent update to 7.4.1.0 having some kind of conflict with the hosting (and possibly Litespeed Cache on that hosting)

1. Update Microthemer to 7.4.1.0
2. Attempt to log in to wp-admin (which appears normal)
3. Error- There has been a critical error on this website.
4. WP admin is not accessible – critical error
5. Front end is initially fine and admin bar is visible
6. Purge Litespeed Cache from front end from admin bar and site crashes with critical error but only because it reverts to the admin link /wp-admin/admin.php?LSCWP_CTRL=purge&LSCWP_NONCE= on clearing Litespeed Cache. Front end still accessible if accessed direct via any url or menu link from front end.
5. Disable Microthemer via CPanel > File Manager
6. WP-Admin back to normal, front end back to normal.

It is only happening on some reseller accounts on one of the hosting companies but it means I cannot update Microthemer without crashing the back-end on login. Obviously that means having to choose between working on the site and disabling Microthemer.

Given the recent update, is there anything obvious that I should be looking at when troubleshooting the hosting issue that I am guessing is behind the problem?