2.What should I do if the S15 works abnormally?

Force power off and restart

When encountering some crash or abnormal situation, you can turn off  AC power switch in the rear panel and restart the S15.

How to optimize the system  stuck problem after using S15 for a long time:

Go to System Settings - Storage - Free up space

When FiiO Music APP is running incorrectly:

Go to System Settings-Apps-FiiO Music-Storage & Cache- clear the storage.