K1c WiFi often fails

I have a relatively new K1c. Most of the time it connects fine with Creality Print (CP) 5.1 and .1. However about 10% of the time, CP says the printer is offline. Even if I power-cycle the K1c, it remains offline after restarting.

I know its IP address, and I can ping it successfully from my Windows 10 Pro PC and also from my Linux server, so it’s clear that the printer’s WiFi is working.

Why won’t CP connect to the K1c sometimes? Has anyone else had this problem? Any solution?