Can't get stable connexion on hotspot when wlan1 antenna is plugged

[Dakyne]

Hi!

The wifi connexion is "hopping" when the external antenna is plugged in. It's an Alfa antenna for long range wifi from my neighbors to my holiday home. (They gave me the password by the way, I did not crack any wifi !).
Any ideas on how to correct this ?

dmesg gives me some errors about brcmf with and without the external antenna plugged in.

"Hopping" means I get a connexion for 2-3 seconds then it disconnects and reconnects in the 5 next seconds. It does this a few times and then disconnect completely. I don't think it's an issue from this tutorial, but I don't know where else I could ask.

Enregistrement.de.l.ecran.2021-08-03.a.23.12.10.mov

The video is in real time.

Thanks for your help !

EDIT : the behavior is the same if I set my hotspot on wlan1 instead of wlan0