Bad connection for those having great connection at Zoom

Hi,

Today we held a meeting first at Zoom, then switching to our own hosted Jitsi (AWS Ireland). There we 2 participants (UK based) how constantly had 'bad connection indicators (red icon) and very low resolution, while on Zoom their connection was perfect.
The were both on laptops connected to Wifi.
As we host on AWS Ireland and Londen is close to that, latency shouldn’t be a problem… so anyone has any idea what is causing these bad connections with Jitsi? Any ways to debug?

Thanks!

Regards,
Rick