I think you'll find the CID signal is being sent outside of the normal window of 500 to 1500ms after the first ring. A CID box doesn't care but a number of phone systems do.

You might ask them to check. I'll guarantee you if you hooked up a POTS line from Bell the CID will work correctly. I've dealt with this exact same issue dozens of times with multiple phone systems (especially Tecom and older Vodavi). The most annoying part is when I show the CLEC that their caller ID isn't working but is on the Bell line, they deny having a problem. To them if a cheapo CID box works then they're good to go. Even using a Viking CID generator to prove to them the KSU is good doesn't sway them.

Here's a post from a couple of years ago when I first started dealing with these CLEC CID issues. Things haven't improved much since then. :bang:

https://www.sundance-communications.com/cgi-bin/ultimatebb.cgi?/ubb/get_topic/f/2/t/001901/p/1.html