Rapid Swimming and Glass Surfing

Today I got some cherry shrimp, and I drip acclimated them for 4 hours. During acclimation they seemed fine - calm, grazing or staying still. Toward the end I moved them to another container to float in the tank to match the temperature - and they seemed fine until actually swimming into the tank. Since I added them, they've been swimming rapidly for about an hour - some are calm, but the ones that are swimming like this are all large and some female. They're skirting up and down the glass and swimming like mad. I'm not sure what happened since I waited until the tests for the water the shrimps were acclimating in and the water in the tank were the same, and temperature checked the water too. None have died yet but I fear if I do nothing some will be by morning.

I'd like to know what to do in response to this, I'm finding too many resources that tell me what I should have done (and to my knowledge have done) instead of what to do in response to their stress.

Lights are off. Nitrates, Nitrites and Ammonia are 0. Tank has been running for over 2 months with breeding snails and nothing else, entirely sure it's cycled - despite feeding snails etc, ammonia has been 0 or close to 0 for a month. Biofilm and algae on a bunch of driftwood, plants are growing fast and well. There is a large open area in the center of the tank but there are taller plants, rocks with holes (dragonstone etc) and lots of driftwood space to hide.
pH is 7.8, GH 8, KH 6, dechlorinated etc.
Has a large filter but have switched this off because I thought the flow would stress them out. Have an airstone and sponge filter running.