@Vincent-TP Ok, so it clears up the following; The release notes forbid people to downgrade from 5.3.3 to an older version, but it's simply impossible due to code changes. So that's an incorrect...

@dagoosemusic That's an interesting find. But actually it doesn't say it's not possible, it's forbidden ! Is also mentions an added enhancement by encrypting the firmware. So I'm thinking out loud...

@Guichanism Hi, I've received this firmware for testing purposes regarding the disconnects of several devices. According to TP-LINK staff, it's a firmware developed specifically for my use case...

Yes, I received a link where I can download this beta 5.2.90.

I've updated the living room AP with this beta firmware 5.2.90. Will test for about a week or so how this works out.

Thanks Vincent. E-mail received and I've replied with the requested attachments.