I answered it with : 会社を休むこともある
But got it wrong(got 0 points), with a note telling me to use かもしれない instead.
I understand that you can answer with the かもしれない format, but wonder why こともある is incorrect.
These are examples I took from the internet :
Basing from these, I think it's safe to assume my answer is not wrong...
Edit: I went and asked my teacher, and although I don't understand the whole explanation, I think I can understand why my answer might not be correct :
The said sentence has a reasoning clause which is 最近とても疲れやすいので. It would only make the most sense when the line is told to your co-worker, or family with the goal to inform in advance; In the near future, you might take a day off depending on your physical condition.
I guess it's similar to saying 明日の天気によっては、試合が中止になることもある where tomorrow's match is a one-time thing. The こともある hinted multiple occurrences in the past and the coming future. They don't match, so saying 明日の天気によっては、試合が中止になるかもしれない is better.
If 最近 is replaced with words to mean like ずっと生まれから疲れがちなので, then こともある will be correct.