Connexion quality

Hello, we have been using “meet.jitsi” for conference calls since last march, We are usally between 4 or 12 persons. we don’t understand why since september, the connexion quality is not equal. Sometimes, few of us can’t connect to the plateform whatever time or day.
Please, Is any anyone may explain how to solve this issue?
thanks a lot for your help

I seond that question on audio and video quality especially, using meet.jit.si on Firefox for Mac Catalina.