I have a deco mesh system and there is a problem with viber videos. They do not download.

The topology is:

Starlink v3, then a tp link TL-SG108E switch. In the switch three X20 deco are wire connected and after that there are two more wireless X20 decos. All decos are in AP mode.

When I try to download a viber video, it does not. If I temporaly switch to airplane mode and then back to deco wifi, then the video downloads. But only this one. If i try to do the same with a second video, the second one does not download.

I tried everything (removing security, disable smart DHCP, adding a guest wifi, restarting everything) but the situation is the same. Decos are also updated to the last available firmware and viber version is the last available.

If I change to starlink wifi, there is no problem. Viber videos download perfectly well.

Finally I added an older tp link access point (TL-WA901ND). I connected this with an ethernet cable to one of the decos. By connecting to this older AP the problem does not exist. Viber videos are downloading without problem.

So, my conclusion is that something goes wrong with the deco wifi (or I missed something) but I cannot figure out what.

Any idea about this?