When receiving shipments of fish regardless of who they are from, I would not go through the normal acclimation procedure. Of slowly adding water to the bag every 15 minutes, for an hour or so. At most would float the bag in the water for a bit to adjust for temp, then release the fish. Really depending on the temp difference, which this time of year can be negligible depending on location you could release them right away.
It is just adding more stress to already stressed fish, sitting in a bag of water with ammonia building up then when you open the bag and off gas the built up CO2 the ammonia becomes more toxic to the fish as the ph rises with the off gassing of CO2. Especially ordering that many fish all usually in one bag, you are going to have some dead ones, so it is the lesser of two evils IMO to let the fish adjust in water that is cleaner (your pond water)than the bag of water they have been sitting in for 24 hrs.
The myriad of issues showing up now could very well be from being severely stressed during shipment, then sitting in the bag water another 2 hrs during the acclimation procedure. This can put them over a tipping point they can’t recover from.
At this point maintaining your water quality is about all you can do, and hope some recover.