PvZ GW2 XB1 achievements issue

I was playing earlier and went into the mystery portal. Suddenly several achievements that I hadn't yet completed unlocked, and I was awarded countless stickers and bonus coins for no obvious reason. On my achievements list, it now shows nearly all as unlocked... however most of them don't reflect in my gamerscore.
Is this a known issue?? I note there was an XB1 update earlier today... would this have anything to do with it??