sometimes get no signal from trainer

I have tacx vortex trainer, I have been using it for last month, it is about a week (i train every morning for 30~60 min) that sometimes, suddenly, the power shows zero in zwift during the workout plan for 5 ~30 seconds ! then again normal
sometimes it happens only @~5 times, sometimes even more than 10 times!!
the point is, I think it should not be from ANT+ usb dongle because I also have garmin cadence sensor and tacx heart rate sensor and they are good and no disconnection!
I thought maybe the tacx gets too hot, I used a fan, but still, i have the same problem!
any idea?
thank you 

You may want to try connecting via Bluetooth instead as a test. If the same issues happen over BLE, it may be a trainer problem. If they don’t, then it’s likely ANT+ signal dropouts, and you should go through our troubleshooting steps for that.

If you’re still having problems, let us know!

Like many other Ant+ users I suffered the same.  The issue was the distance between the Ant+ dongle and the trainer.  Buy an extension lead and I’m confident your problems will disappear.