Hey Gerrie,
thats a good question.
Is there a fps counter in Zwift?
It felt fluid but honestly we very more worried about the watts in that situation and ended the ride soon.
Scince the problems occure on my buddys laptop who lives in adifferent city I have to get back to you when I have the log file - hopefully I will know more this afternoon.
Also I found the blog post on Zwift Insider where Eric recommends the Anself and Suunto dongles.
I consider ordering those just to make sure the problem is not with the dongle.
Cheers,
Thomas.