The phone is always on 4G, and the speed of the internet from the router is 420/63 Mbps; this is more than enough. I also have another brand of indoor security camera, which I can access from anywhere.

Hello,
I have 5 RLC-510WA cameras and 1 E1. Everything works fine when I am in my country, but when I go on vacation, the cameras connect very slowly or most often do not connect at all. This happens regardless of whether I have a WIFI connection or a mobile data connection. All cameras are updated, and the applications are also updated. The situation is the same in both applications. The internet speed is always at least 20 megabits, usually around 50 megabits or more. What could be the solution?
Thanks for help