YouTube app bug "Connection to Server Lost"
Clear cache and data of YouTube and Google play services. It is recommended to do this provided you have a high speed WiFi/data access. These apps may download approximately 70-80 MB after clearing their data.

Steps:


Disconnect all data connectivity. i.e. WiFi &amp; mobile data.
Go to your phone's 'Settings'.
Click on 'Apps'.
Scroll down to YouTube and click on it.
Click on following buttons in order: 'Force Stop' > 'Clear Cache' > 'Clear Data'.
Press 'back' button to come back to application list.
Scroll up for 'Google Play services'.
Do same again in order: 'Force Stop' > 'Clear Cache' > 'Clear Data'.
Restart your device.
Switch on your data connectivity. i.e. WiFi/Mobile data.
Open Play Store and wait until everything successfully loads up.
Now exit from Play Store and open up your YouTube app. It should probably work fine now.