I finished the event missions that gives you 5 lootboxes, making it a total of 10 counting two missions that gives said lootboxes, but while opening them, my count for a guarantee legendary lootbox remains at 8, I should have like 11 or so, counting 1 extra lootbox from the weekly rewards I just had.
this also happened to me but I think it resets to 0 if you get a legendary from one of them 