Joachim, sorry for the troubles. Were you trying to pair over ANT+? I wouldn’t say it’s particularly common, but on the pairing screen near the top left will be a status icon for the ANT+ dongle. If it has a ’ ! ’ on it that may indicate we couldn’t get access to the dongle. Common cases for that might include having other ANT+ software open (garmin, for example) that has taken control.
If you didn’t have any exclamation point on the status icon, then it might be worth unplugging the dongle and replugging it back in (while Zwift is running at the pairing screen) to see if that resets it.
If this happens again, grab your log.txt file from Documents\Zwift on your computer and shoot it over to our support department and they can dig through it to see what might be going on.