Hi,
We are playing Bob's + Angel's game, and run into a problem of coolant temperature change. The problem is not consistent and difficult to catch. The issue is there are no stations supplying cold used coolant, only 300C. But the temperature of the coolant at requester stations keeps dropping below 300C. We are confident there is no cross contamination in the local setup, which leaves the drones as the only possibility.

I can confirm this happens. Used Coolant (from Angels) temperature drops from 300 to lower temperature. This makes coolant based recipes in Angels basically unusable with drones, as Angels cooling tower only accepts Used Coolant in three temperature intervals: 85~115, 185 to 215, and 285 to 315, and the temperature drop induced by Transport Drones would eventually settle the temperature at something between 125 and 285. Then the whole cooling set up just stalls. It's a rather serious conflict with Angels.

Can you provide a save game showing the setup?

The drones can't really tell temperature when deciding what to pick up

Sure. Here is the link: https://drive.google.com/open?id=13gPSeVL3sK7DB0E62UoAPED6xZlD-WIs
I labeled the problematic complex on the map

For whomever faces this same problem, I created a mod that fills in the gaps of temperature. With this mod the same three recipes cover all temperature ranges, can be used as an alternative:
https://mods.factorio.com/mod/angelscoolanttemperatureextension

Ok I think I managed to fix it

Thanks!