How do you distribute the power and signal across the pairs in the UTP-cable?
I mean, do you have one pair for power & ground and then a single wire for the data and if so, what do you do with the other wire of that pair?

I'd probably start with it grounded but I don't KNOW that's the best way.
Perhaps using BOTH wires in a pair for the signal?
Or run power and signal in one pair and both wires in another pair for ground.
Maby a capacitor across power and ground at the far end of the cable?
If the error(s) doesn't occur TOO often perhaps a simple retry is enough?

Just tossing ideas up in the air, perhaps one or more helps, I don't know :-)

I understand the "trickyness" in making this rugged if the bus topology is to be decided by the end user. I think you need to specify like max 50m length, each sensor connected to the main trunk by max 50cm - or whatever. Set that up with margin and test.