It is probably normal. I have seen mite populations change with no apparent reason.

Mine has gone in the opposite direction - from a couple of short term mite attacks in the past 2 years, I am undergoing an attack that has lasted for a month.

Have tried leaving top open at night, letting bin dry out a bit, rinsing top daily (dots all over - I rinse in driveway!)and using my BBQ lighter to burn the dots on the top of the paper! I have water mister bottle handy! But still have a lot of mites.

I have read conflicting reports - that they are bad for my worms and will vampire them to report on redworm composting site that they do no harm.

But it grosses me out when it looks like mites are on the worms

Take a closer look at the activity. Are the mites just consuming a dead or dying worm? My understanding is that they eat decomposing (dead) organic material.

rom.calgary.ab:

Nope, the worms are alive. This summer had been warm - so I'm hoping our winter (haha! I'm in Hawaii) cool will reduce the mite population.

Winter here (AB) does a good job of reducing a lot of critter populations.

Mites like it when the bin is acidic and wet. Try adding some calcium carbonate or crushed egg shells and let the bin dry out some. That will help. You could also put some double-sided sticky tape around the top edge to trap some.

In regard to the original post, that certainly is puzzling. I've always got mites. I mean, it is as though they appear in droves in a matter of hours even in new bins. Your climate isn't that different than mine.

I prefer the mites. They break down food that can take a little time to break down.