Ask an expert

I have recently taken my vehicle to get a CVT service but after checking the transmission fluid level, I believe they have overfilled the transmission to about 20mm above the mark on the dipstick when cold. I have been experiencing a "shudder" as if the CVT belt is slipping on take-off and under load.

Is this problem indicative of running on an over-full CVT? and if so, what damage could this cause?

I wouldn't think that over-filling it could create this problem. However, make 100% sure the correct fluid has been used. We often hear of normal ATF being used in CVT's, and this can definitely causes problems.
The best advice is to take it back and get them to check it out. If you've any doubts about the original service agent putting the wrong fluid in, maybe get an opinion from another trans shop first.
You don't say whether or not the shudder was evident before the trans service or if it has only become evident since. However, if the correct fluid has been used and the problem has only started since the service, it could be coincidental.