Skoda Citigo transmission issues

Sounds like a right pain. Had something similar happen with my old Renault Megane, though it wasn't exactly the same. The gearbox kept slipping and throwing up all sorts of warning lights. Have you checked the basics, like coolant level? A coolant leak can mess with the whole cooling system and cause all sorts of weird issues. Also, maybe have a look at the cooling fan, see if it's kicking in properly. Is the pressure gauge behaving as expected?

Coolant level is fine, and the cooling fan seems to be working okay. The pressure gauge seems normal too. You mentioned a similar issue with your Megane – was it also related to the radiator or something with the transmission? Anything specific I should be looking for?

Yeah, with the Megane, it turned out to be a faulty sensor connection related to the automatic gearbox. It wasn't directly the radiator, but it was messing with the transmission's understanding of the oil temperature and pressure. Caused all sorts of mayhem. Given that your garage already suspects a cable or plug connection, I'd say they're probably on the right track. Honestly, best bet is to get them to properly diagnose it. Could be something simple, but messing with automatics without knowing what you're doing can get expensive fast.

Just wanted to close the loop. Took it to the garage as you suggested. Turns out it was a dodgy connection on the radiator oil pressure sensor, just like they suspected. 95€ later and it's shifting smooth as butter again. Cheers for the heads up!