It may take the speed reading from the gearbox and this can happen when the drive is worn.
From memory, it is easy to remove and check to see what condition the worm drive is in.
Follow a thick drive cable into the top of the gearbox (could also just be a wire going onto a transducer but will still have the same plastic worm drive).
Worst case scenario (which we used to have on Rovers) is when the final drive bearings drop due to wear and this can also make it jump
Hope you are all making the most of lockdown.
I went out in my Astra G this evening, first time in 3 days. And the speedo is all over the place when maintaining a steady speed or slowing down. When pulling away and building up speed its steady. Have read that it could be the ABS sensor in the hub. I dont have ABS.
Could this be the hub dying or just a dodgy connection?
Thanks in advance.