Try deactivating and reactivating it.
You might try chatting with Verizon and asking them to confirm that your caller ID service to the FiOS STB is using UDP, not TCP. Some accounts use TCP which is very unreliable. Mine is set to use UDP (Listener 1) and I never have any issues with it not working, except occasionally when telemarketers spoof caller ID in which case I don't even get the caller ID on my phones. You can check which "listener" your STP is set to and infer whether it is TCP or UDP by running the Customer Support>>Top Support Tools>>Self Diagnostics check on the STB. It is listed under the FiOS TV Remote DVR area. Listerner 1 is UDP and Listener 2 is TCP.