I had the same issue recently ,my visa was issued a few days after my flight . I entered Thailand for 30 days visa exempt(uk passport) then flew to Vientiane and had a couple of nights on the razz and reentered Thailand on my visa. No questions asked. Ok it’s a bit of extra expense but at least you can stay an extra 30 days (or 60 if you extend your visa exempt entry) as your visa will be valid for entry to Thailand for 90 days from the date of issue.
If you have it then you can but it’s not actually a requirement for the original 90 day single entry visa so it doesn’t matter how long it’s been in your account. I got my visa last October only showing about £1500 in my bank as I was waiting on the proceeds from a house sale.
If your talking about the 90 day visa rather than the 12 month extension there is a problem with the on line application. I was told that the 400k baht is not required for the 90 day visa and had to upload a document saying simply “not required” in order to work around the error.
I recently sold my house in the UK , it sold within 24 hours and I was on the plane to Bangkok 6 weeks later. That’s best case scenario though in all honesty.
It’s only a requirement for people who will travel to a country that requires a covid test as an entry requirement so unless the uk changes their entry requirements then it won’t be an entry requirement in Thailand.