So, this just got resolved positively:
We got a solicitor involved, they recommended:
For both, knowing what information exactly UKVI used for their previous decision would be quite useful, and that can be obtained for free with a subject access request.
Instead of waiting on the SAR documents to get back to us, my SO submitted a new visa application right away (with the information that has been provided above in the question and a cover letter). The decision was positive in this case and the visa has been granted (which means that luckily plans didn’t have to change),
Though this means that until we’ll see the SAR documents, it will not yet be clear if they had any wrong records on their side or what was actually the explanation for the last refusal.
I might update this when I’ll get that information, and I could also provide a (redacted) copy of the cover letter, if people could find that useful.
Update:
This is the cover letter, attached with the latest application:
We also got the SAR file, and I got 2 interesting findings:
Credit:stackoverflow.com‘
5 Mar, 2024
4 Mar, 2024
5 Mar, 2024