Time Team Help

Here's a silly little annoyance. I power off my PC every night & several times, when I restart it, the time display shows as 4-6 hours slower than it should be. If I go to Windows time & date settings & turn off 'Set Time Automatically', then turn it on again, the time resets correctly and stays corrected. The date is always OK.

Any ideas why?

Win10 home with automatic updates.

 

Replace the CMOS battery. This keeps the time up to date when the power is off.