Most likely, it is a connection issue - the connection between your trainer and your computer disconnects. You can validate it by uploading log file to Zwiftalizer.com. It is a free log file analyzer which helps people to interpret contents of Zwift log files. It also explains where to find your log file, if you are on a PC. With other platforms, it is also possible but harder.
The most common reasons for disconnects are:
- computer too far from the trainer, so signal gets low
- Trainer is connected to several applications which compete for connection (for example, you may have connected it to Wahoo Fitness app and forgot to disconnect - it does not matter if Zwift and Wahoo Fitness run on the same device, they use separate connection streams).
- Interference with other wireless devices
So, make sure that no other application other than Zwift is connected to your trainer or may compete for connection (e.g., an app on your wife’s or kid’s phone or on a tablet). Reboot your phone just in case, to kill all open apps so that you know for sure what is running and what is not.
Bring your computer closer to the trainer.
Try connecting with a different protocol, e.g., ANT+ if you have been using BT and check if that would better (if you an Apple user, then… well… most likely it is not an option… I am sorry).