"But if you use the WAN and LAN ethernet ports then it is a major difference!"
I don't understand this, for me doing a speedtest between LAN and LAN is nonsense.

The fact is that it works perfectly in Access Point (bridge) and also that it was working perfectly before, but I don't know why and I don't know with which version it was (beta or not)

And so why are you talking again about what is not for me ...
"Usually happens when different network types are mixed" I mix which different networks ?