So apparently QTH still works but it does occasionally spew errors. I am uncertain if they break any functionality but nevertheless...
One of the errors I caught was:
[Error]: (QuestTrackerHelper): Script Call failed - Error while calling [QuestTrackerHelper.QuestUpdated]:
[string "Interface/AddOns\QuestTrackerHelper\QuestTrackerHelper.lua"]:182: attempt to index local 'Quest' (a nil value)
Could anyone with slightly higher knowledge in lua/html than me (i.e. knows anything at all) look at it and propose a fix please?