Thank you Howard, sorry about the brief issue description! I can do better...
What I did:
1. Run the usual plugin checks.
2. Updated available plugins via the plugin overview page.
3. All plugins "passed" the checks except for the gapfill question type. It stated it needs a newer version of Moodle which I don't want to upgrade to yet. I keep getting stuck at the plugin upgrade where the system cannot go forward due to the incompatibility of this new plugin. (I'm surprised it allowed me to upgrade this plugin - I have raised this with the developer already).
So I have checked the /question/type/gapfill directory - it contains all new files dated a few hours ago. These I assume are the folders/files triggering the update for this plugin.
What I propose to do is:
a. rename the /question/type/gapfill folder to /question/type/_gapfill_backup
b. Upload the previous package again as a zip file via this URL: (mysite)/admin/tool/installaddon/index.php
c. since I've renamed/backed up the newer version it should hopefully cancel the upgrade.
Do you think this will resolve?