Hub v3 Internet stability requirement if any, or something else? EU version

Does anyone know if the v3 hub requires a super stable internet connection or something for pairing?
The Story: I have 4 hubs in the US that have been fairly stable and easy to connect devices to. So I think I know the most common tricks for pairing stubborn devices. But maybe not.
I purchased another hub in the EU (France) with the EU frequencies for use there. I had the hub plugged into my network which uses 4G cellular to get a internet connection (very common there). I cannot get zigbee devices to pair there. I have moved the devices close and not so close to the hub. I have moved the hub into a room away from the WiFi router. I checked the channels to assure that the zigbee and WiFi were not fighting. Yet I could never get the devices to pair.
I brought the hub back to the US and plugged it in to my network here (Fiber) and then plugged a couple of the different devices into a 110/230v transformer and they paired just fine first try.
Does anyone have any suggestions as to why this happened? And how to pair the devices I left in the EU once I get back?

Can you try a different hotspot with a different mobile network?

Since SmartThings is primarily ckoud dependent, I would think stable internet would be required for ading devices. However, assuming your network had decent 4g cellular signal, I would think that would be sufficient. Did you try any z-wave devices while it was on the 4G connection?

Sorry for the late reply.
I use the current 4G modem for everything else at the EU house and have never noticed any lag or drops. I do VOIP back to the States with no issues.
I will be able to retry pairing the other Zigbee devices next week but I haven’t purchased any EU Z-wave devices as they don’t seem very popular there and the prices reflect that. I would take a spare back with me but my understanding is EU z-wave is not the same as US z-wave.
I do have an Orange SIM and a Free SIM so maybe I will try swapping them to the modem as a test. I am using a ZTE stick modem plugged into a AC68U and did try swapping the USB ports with no luck. I am going to purchase a Huawei B818-263 on my return and see if that helps too. Its supposed to be pretty good and does have a bunch of aftermarket add-ons to monitor connections and stability.

Correct, the radio frequencies are different. The hub and The end devices have to match frequency exactly or they can’t talk to each other. The UK and the EU use the CEPT frequency.

https://products.z-wavealliance.org/