@Raymond
The limits for Azure File Sync are published here. It is possible you were hitting one of the limits. There is a hard limitation of 30 server endpoints per server which would make your scenario not possible.
Hope this helps. Let us know if you have further questions or issues and we will do our best to assist.
-------------------------------
Please don’t forget to "Accept the answer" and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.