I think this is the right category, but I could be wrong. On the site currently it isn’t displaying my most current mention in the interactions section. I can toggle between both the interactions and mentions sections and it will show and then dismiss the latest one.
I’ve posted a similar issue at https://dev.twitter.com/discussions/15477
My theory is that some mentions are being filtered out of Interactions if the sending account is deemed of low priority in some way. Has your issue reoccurred? Would the sending account fit the low-priority profile?