Had same problem, not sure now, did not look at, get use to it even its bit bad...
Bigger problem for me was when a buff didnt accepted. I see how a building is missed, but my buff teammate says its ok and buffed... so I go to visit someone and when I come back I see all buffed...and again I stay online, but at evening I turn PC down, tomorrow come back online again and I see how, not only that buildings, but also some new buildings didnt accept the buff. Most of the cases it is in S6 of my Island and some in S1 or Archipelago.. I have this problem maybe couple of months now, even before this one with highlighted after being buffed. I checked this several times, tryed to logoff - login, clear this and that, but as far I noticed, will be visibly only if Im offline when main server do refresh and new daily tasks occurs at 03:00h in the morning.