So did you set up the 400c radios from scratch or did you upload the config from the 550’s they were replacing ? I replaced a 550 link with 400c and just uploaded the config from the 550s to the 400c’s and even though everything appeared to go fine there were some problems caused by that. I ended up defaulting the 400c’s and reconfiguring them from scratch.
Otherwise maybe try rebooting or up/down grading the firmware oorrr the ever popular ePMP ritual of deleting your browser cach/cookies/history or open the radios in a different browser that has never opened up radios at those addresses before (and thus should not have anything cached/saved for them)