I’ve re-loaded the program and zwift mobile link several times - avatar moves slowly for 3 seconds and stops. I have a computer that’s 3 years old and a Samsung phone that’s 3 years old. Are these not new enough devices to work with your program?? Moved and recalibrated the speed/cadence sensor several times, and STILL, the avatar does not move faster than a crawl, even though the computer screen is saying my avatar is moving at 18-20 km/h. I have spent HOURS trying to get this to work. What a disappointing experience.
In order to help you we need some more information. What trainer are you using?
You can always log an official support ticket:
Please add some .log files that can be found here “Documents\Zwift\Logs”
Probably something is wrong with the communications between the trainer and the PC. Zwift runs fine on my 8 year old PC running 64 bit Windows 10.