no no i thought she / he had cheek osteotomy. cheek partially is a maxilary bone, behind it the sinus
I just imagined, that the maxillary bone has some no healed fragment, little gap / hole and some bacteria and viruses get into skin
but it's probably almost not possible
i think the only one thing which can make constant swelling is foreign object, which must be removed in such case
other possible option... just nervous reaction
i do not know... you say it's not so rare.. so it's strange. I could believe if it was very rare..ahh
i got one thing
perhaps if you have bad reaction to plates, then after removing you have still allergens in your skin / fat.. The body must to dissolve it which may take several weeks I see this in that way.