The electric locos from "Realistic Electric Trains" (https://mods.factorio.com/mod/Realistic_Electric_Trains/) are "working" .. but the drive just around ~100km and "fuel empty" is blinking.
have tested some setting with balancing fuel, but just the same
It looks like they might have changed some math in the moat recent version, which would throw off my calculations for the double-power version. I'll take a look.
The symptoms you describe match an issue we had several versions back but it appears to be fine for me now with everything at the latest. Here are some things to try:
With two locomotives both pointing forwards, can they run normally?
Does the electric grid have enough power to supply the locomotives at full speed?
Can you post a log file with what mods you are running, and maybe a save file of this happening?