Hi and Welcome to the forum.
😎I would suggest to make sure your on the newest firmware and also do a simple reboot by turning it off and back on.
Make a back up and possibly try a Hard Reset to see if that helps.
The link to show how is here ->
http://www.hard-reset.com/htc-one-sv-hard-reset.htmlIf no joy look at HTC's support pages via
http://www.htc.com/uk/support/htc-one-sv/troubleshooting/ then d if no help I'd suggest speaking to HTC UK Support via
http://www.htc.com/uk/support/ as they know their hardware / software possibly better than a 3rd party repair centre.
The best of luck and I hope your phone is back up and running asap.
😎
Current Phone >
Samsung Galaxy s²³ Ultra 512gb Phantom Black.