If i participate in events then there is a big timelag between my actual route position (=what i see onscreen) and what is fed to my trainer. The trainer (newest Kickr) can have a lag of multiple minutes (!).
So when i have started Alpe du Zwift, i actually only start feeling the resistance minutes later.
This lag seems to increase with the duration of event too: so the lag builds up gradually.
If i just do a soloride it seems fine.
Has it to do with load on internetconnection: that an event requires much more load (eg updating position of other riders etc)? my connection is pretty avg (25MB/s).