I now have everything (gateway and all sensors and yeelight lamps... 20 in total sensors and lamps) under Singapore server.
I did it using an android phone.
Mi home is version 5.1.29 and gateway has firmware version 1.4.1_154
I found some time to try again after my last unsuccessful attempt last week (but this time with updated mi home and gateway).
The first try was again unsuccessful, i did a reset to the gateway and then logged in to the Singapore server but the gateway was not found, then i left the gateway in reset mode and i logged in back to Mainland China and directly back to Singapore server and the gateway was found. I added it without problems this time and it initialized without any problems!! (EVERYTHING is working in settings). I had the issue that the light turned green after a few sensors but this was solved by taking the gateway a few seconds out of the ac power.
I didn't even need to add the sensors again. Every time that i used a sensor (either pressed a button or pass in front of a body sensor or open a door with a sensor), it was found automatically just because it was already added to the gateway to China. The Humidity sensors just needed a few minutes (enough to send a reading) and they were found also.
The only sensor that wasn't found automatically although i pressed it was one of two aqara switches (Oh yes i forgot.. aqara switches work perfectly and recognized as AQARA). So i had to add it manually and it was added without problems since aqara switches ARE now included to the child devices of the gateway!!
After that i did a reset to the yeelight bulbs and added them to Singapore (using mi home..) and then created all automations for the switches (single. double, long press) and everything is working PERFECTLY.
Tomorrow i will fix the rest of automations but everything seems to be working perfectly!