Having the same issues detailed above (consistent drop outs on group rides) with my Microsoft Surface 3 Laptop (only a year old). Not sure if its disconcerting or reassuring that so many are having the same issue.
Welcome to the forum.
You can put you log file in Zwiftalizer.com and look at your network connection
Integrated Intel GPU?
I seemed to fix the issue by changing my battery settings to run at lower performance and had no issues for the last month. However the issue reared its head again when trying to ride makuri islands (which is what it did previously now that I think of it), it may be a complete coincidence but has raised some suspicions. Since that point the crashing issue has come back to group rides as well.
Yeh, Intel Iris Plus.
It might be that the laptop is not powerful enough for Makuri that world os very graphic intensive.
Set Zwift to the lowest setting possible.
Makuri has certain areas of the map that even bog down very high performance gaming machines.