So, I got the good news 3 days after posting here that my Application for LTR Wealthy Pensioner was approved.
Since I submitted everything on September 1st (and was never asked for any other documents, it takes way more than 20 working days to get an answer these days...but I also know from a friend it went faster for him a few months ago.
My advice, if you live in Bangkok, is to go to BOI in Chamchuri to have them call the government agencies to figure out your status ( I did it twice).
I also sent an email last weekend through the BOI platform ...and received an email back from them 3 days later saying it was approved, with a detailed explanation about the process. I just need to update a few documents (the last passport-stamped page, and a medical certificate but for this one, my understanding is that it is only required for the category with work permit).
So al good !
As said above, yes you can visit BOI in Bangkok as much as you want, you can also call the BOI number to get some information/updates about your application