I put "during meals" because "often" implies in general. Is this really wrong, or is the French discussing ONE meal (which repeats periodically)? Sorry if this question is hard to understand.
Singular or plural could be used in real life: "pendant le repas = pendant les repas".
If Duo proposed a singular, you would need to stick to it in this case.
In French we're talking about any meal that his father takes.
Any meal at all? Then in English, it should not accept "during the meal" as that specifically excludes the possibility of "any meal at all".
Then the english translation must be plural. Otherwise it's just one specific - and I presume very long - meal.
I agree, to maintain the same meaning in english duolingo should accept 'meals' in plural