Considering ‘MODULE_NOT_FOUND’, your update process might not have gone smoothly.
Maybe your server used up available RAM during the update process, this led to the update getting stuck.
This error could be caused by incorrect permission of directories and files, incorrect path or really by the absence of some module.
There are reports of a similar issue here on the forum: Unable to start Ghost.
I believe that, if it was an error related to the permission of files and directories, the ghost doctor would have reported it.
You may be able to momentarily stop some non-essential services to complete your upgrade. (To get more free ram memory).
You can force the update to try to fix possible missing files:
ghost update --force
You can also go back to the previous version by running:
ghost update --rollback
Tip: I’m not sure if ghost does a backup before updating, but you can do that manually by running ghost backup.
You can read more about this in Update Ghost to the latest major version.