Thanks for the information. After checking my router configuration, there might be a problem with port forwarding configuration (because we are not using port 443 publicly to get to rei3). I think we might find the solution for now. We'll try for several more days if it's solved, but for now it seems to be solved.
The issue was REI3 was responding ok at first. Then at some random time ( I cannot find the pattern) after I save some things in the builder, the save button never turns grey. And after that it seems that I cannot save anything else (not responding). However, if I close all windows and log in again, everything seems to be ok and the last saving was saved ok. The REI3 service seems to be running ok instead all this.
Anyways, I hope we correctly identify the problem. Let's see in several days.
Thank you for the pointers. Love how fast the REI3 team respond to questions.