What firmware is the 120 on and what MRU have you got the 120 set to? 1492 is UK's, and I see there is a 1500 popping up.
Coincidentally, I was supporting a now ex customer with similar setup and you would be the right timescales away to be the one's who took over from them, hence the "coincidentally" amongst other things, of course knowing what the spooks know, you could just be a spook playing me. ;D
Edit. This might also work for you. https://forum.pfsense.org/index.php?topic=86087.msg473517#msg473517