I also suggest that you read this thread: Problème de connectivité intermittent - #25 by Jami. I translated the following content from the original that was recently written in French by a Jami admin (the original message is more detailed - you can use an online translator if needed).
[…] Jami is a distributed communication software, so by definition it cannot work in a very restricted network environment. At the very least, the following ports must be open: FAQ - Jami documentation
If this is not possible, the only way to use Jami on a very restricted network will be to deploy DHT proxy and TURN servers inside the organizational network (or on a DMZ).
[…]
As you can see, this is not something that the team of Jami developers or a simple user of the restrictive organizational network can do. This is an infra/network architecture project that the organization’s IT managers must carry out if they decide to use Jami.
I have this problem on my institutional network where most UDP ports are blocked and where Jami is therefore unable to connect to peers. I checked with my laptop (dual boot Win11 and Linux Zorin 17.3 OS): no problem on my home network, but alas 
impossible to use on my work network. If you have a laptop, I suggest you try if the problem applies to you. I suspect that several users who have problems with Jami on work networks might also be confronted to the same issue.
UPDATE 2025-04-16: There is a way to overcome the problem by using a VPN like Mullvad, see Problème de connectivité intermittent - #27 by mmms