watchtube application disappeared once re-pairing completed

Hello reverse2010, 

Thank you for posting to the Apple Support Communities. 

We understand that you may be noticing an issue when installing a specific app to your iPhone and Apple Watch. We’d be happy to help you evaluate this situation and find a solution. 

To get started, it would be a good idea to confirm that you have the latest software updates installed for your watch and iPhone. The following Apple Support articles explain how you can back up and update each device: 

Update your Apple Watch - Apple Support

Update your iPhone or iPad - Apple Support

If you continue to notice the same issue after updating, please use the instructions from this article: 

If you can’t download or update apps on your iPhone or iPad - Apple Support

You may also want to contact the app developer directly for help confirming that your devices will be compatible with the current version of the app: 

How to contact an app developer - Apple Support

If you are unable to find a solution using the suggestions above, we would ask that you contact Apple Support directly for more help. 

We hope that this answer helps you. 

Have a great day!