This is a weird interaction with https://mods.factorio.com/mod/Ultracube . Ultracube has a tech that vastly increases train speed if the train cargo contains the ultracube (a unique item). For some strange reason, with cybersyn combinator installed, this tech no longer works. The given train remains the normal speed. I took a glance at the source code and nothing jumped out at me, but maybe you have a guess.

Just tested with a minimal set of mods:

• Project Cybersyn
• Cybersyn Combinator
• Ultracube
• Editor Extensions (for easier testing)
• (and any dependencies required)

The trains seem to behave as expected, speeding up immensely when the cube is in a cargo wagon.

Do you have a save file to test with? Also might be worth raising an issue on the Ultracube mod page, as they seem to have added specific compatibility code for this mod so they might have a better idea of what might be happening.

Weird... I had disabled cybersyn combinator as a workaround, and now when I reenable it to produce a test save, the speedup buff works as expected.

Please ignore this. Sorry to waste your time!

No problem, I'm just glad things are working again! Don't hesitate to open an issue when you discover something.