Mitsubishi ASX Gearbox & Transmission Problems
Having trouble selecting reverse in a 2023 Mitsubishi ASX
Intermittent problems like this one can be very annoying as they rarely emerge when a mechanic is looking at them. However, you need to have the Mitsubishi dealership mechanic with you for a test drive as you try to make the problem occur, however long that takes. Perhaps you could video the car's behaviour next time it happens and show the workshop that way.
Common causes for a manual car to refuse to select a gear are usually down to a worn, maladjusted or damaged clutch or a poorly adjusted gear linkage. If there's a horrible graunching noise when this happens, I'd suspect the clutch, if not, it could easily be a simple matter of adjusting the selectors. Either way, this shouldn't amount to rocket science in 2024.
Just be sure not to take no for an answer; if the car has a problem, it's under warranty and it's Mitsubishi's problem, not yours.
Mitsubishi ASX 2017: What can be causing it to stutter?
It’s likely to be the CVT transmission, that’s obviously what the dealer thought. You could pursue it further with dealer/Mitsubishi, but I reckon you’re stuck with it.