Unfortunately, I think it's common
My flat wasn't even bought by a first time buyer
But some of the same questions came back several times. My solicitor reverted to saying "asked and answered" because luckily, he is like me in that direct way.
Also, we refused to answer some of the questions because they were just mad e.g they wanted a full set of papers relating to the original planning permission for the building and the demolition of the previous building.
Far too old and I suspect if they asked the council, the council wouldn't have them anyway.
My solicitor thought that it was likely to be mad questions from the mortgage company solicitor, he didn't think the buyer was to blame.
I read up a lot about this at the time and you can probably find it if you just google the quote "conveyancing is now so slow it's going backwards". The amount of things you can sue people for, the amount of things that you need indemnity insurance for... I was supposed to be moving again, but I can't face it. It's ridiculous.
The process is now so onerous it means that I don't want to make another move unless it is my last, which may be a retirement flat
Sorry that was a rant. But that's how I feel about it now.
The good news is, I don't think they're up to anything dodgy!