However, in this case the answer was not marked as having a typo, it was just accepted as correct.
I think this is a bug that's been affecting a lot of users lately, and on all courses :(
Is it usual to drop the accent in verbal nouns?
I'm not sure off the top of my head, I'll have to see if I can think of any others. For what it's worth, 'sgìthadh' is what the dictionary has, but the accent was later dropped in the Gaelic Orthographical Reform.
DuoLingo does NOT accept answers that are one letter out as typos. I have had multiple answers marked as wrong where absolutely the only 'mistake' I have made is to double one letter when I shouldn't have done or transpose two letters or, as in this answer, the apostrophe that I thought I had typed does not appear. It is intensely frustrating as these are nearly all genuine typos rather than actual mistakes. It then accepts things that really are grammatical errors such as when I have failed to lenited a word that should have been lenited.
You have the apostrophe in a ’sgitheadh in the wrong place. It should be after a, not before s. It helps if you put the two sentences (the given answer and yours) under each other, then you spot the mistake easier:
Bidh mi a ’sgitheadh a h-uile latha.
Bidh mi a' sgitheadh a h-uile latha.
I put it every where. After the a, before the s, with a space, no space. It was marked wrong every time. It was extremely frustrating. I gave up 3 or 4 times without reporting it. I couldn't continue my practice until that thing made up its mind. I could only practice the areas that needed practice to reinstate them. I finally typed it out 3 more times before it allowed that I was correct and let me pass, even though I had typed it a' the first time through for three days.