1) Power off phone (be sure to turn off fast reboot in settings first). 2) Boot into recovery by holding volume down key and then holding power key until boot menu appears. 3) Volume down to RECOVERY and tap power key to select. 4) HTC logo appears followed by blank, dim screen. Briefly tap all three simultaneously: power key, volume up and down keys, and release immediately. You may have to do this step a few times to get the timing right. 5) Black screen appears and SD card error message scrolls. After about 5-10 seconds, recovery menu appears (all in very small font). Volume-down to "wipe cache partition" at bottom of list and tap power key. Cache gets cleared. Then select "reboot system now" by tapping power key again (this choice highlighted). Done!
Device will now be a little snappier and some quirky behavior that sometimes develops is fixed. May want to do this every month or so to keep things running better, or if device behaving strangely and you want to try a quick fix that may work.
Sent from my HTC One via XDA premium app