If your device runs out of memory, you may be unable to change your pen type.
Please make sure the device you're using (PC, smartphone, etc) has sufficient space available.
Closing background apps may resolve your issue if you're using a smartphone.
If your issue still isn't resolved, please try the following:
・Ensuring your internet connection is stable (if you're on desktop, try using ethernet over Wi-Fi)
・Clearing the cache on your browser and/or app
・Logging out of Sketch and logging back in
・Changing your browser, app, or device