All 89 bee plants
Himalayan balsam pollen
Impatiens glandulifera
Ghostly white, in the cream / white range.
FloweringJuly to October
PollenGood
NectarYes
SeasonSummer, Autumn
WhereWaterside, Waste and verge
Foragers come home dusted pale white. Invasive along rivers, but a heavy late nectar source.

Easy to mistake for these
Closest pollen colours in our set, measured the same way the pollen identifier scores a match. Colour alone will not settle it, so check the flowering months and what is actually growing near your hives.
Out at about the same time
Saw a load like this going in?
Sample the colour against all 89 plants, then keep a forage record per hive.