Hello,
I have a similar setup with RUT240 (in bridge mode) and pfsense. I have even older fw on RUT240 and it has been up and running for a few years without any problems.
Last week I upgraded RUT240 to latest fw but no matter what I did I could not get bridge mode working again - tried hard and soft reset but nothing worked. It does not bind the external ip from RUT mobile wan to specified mac address, instead you get an ip from RUT lan ip-range.
To me with the updated fw everything seems to work much slower than before (applying settings in gui etc.). As soon as i reverted back to old fw everything works as one would expect.