Same here. My new modem is XB3, at bottom of front face. This was the replacement that comcast installed mid May 2019.
Old modem about 7 yrs old started giving problems. New modem has performed worse. Frequent updates often take an hour to recover after 2 or 3 manual reboots. Wifi and direct connection to pc go down frequently. Often not connected but Online light stays on. Nightmare.
What do the modem's signal stats look like ? Try getting them here http://192.168.100.1 or here http://10.0.0.1
Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.
Good news is that problem was solved and it wasn't the modem causing the problem.
Called comcast and while on phone they were able to test the line from, pole to house and determined it was problem on outside line. Tech came out next day and they replaced the line from pole to house and all was ok after that.
O/k glad you go it squared away ! Closing this thread.