Hello, everyone!
Recently, someone asked me "Why does the ACS fail to connect to the ONT?" Why does the ONT go offline when I query the ONT status on the ACS?
The problems mentioned above are the two most common problems in the current network. When you find this problem you can follow the steps to find why:
1. Telnet to the ONT through OLT.
2. Ping to the ACS from TR069 WAN. And TR069 IP you can check from the U2000 WAN details
3. Open the CWMP debug info. Then connect ONT from the ACS to see if there are packets
Each step is shown in the following figure(The data in the figure is only for display):

I hope it will be helpful for you. Thank you!