- You are running Linux on Hyper-V guest VM.
- Your host machine has scheduled downtime (i.e. is not 24/7 system).
Time Synchronization option on Hyper-V Manager console doesn't make the situation better.
You should sync the system clock with ntpdate, or run
hwclock --hctosys periodically with cron:
*/5 * * * * hwclock --hctosys