Problem with time synchronisation on OPI+2

[Seki]

Hi,

 

I use armbian distribution on opi+2e , in order to operate the Jeedom home automation system. I occasionally encounter crashes of my opi, which becomes inaccessible in SSH. We are several users of this system to encounter the same problems.
In logs, date is 1970, so we suspect a time synchronization problem.
We use timedatectl for ntp synchronization, but it appears that rtc clock (fake clock) is not stable.

Why?
Any solution to keep rtc clock synchronous with ntp?

Somes members of Jeedom community try with hardware RTC clock on I2C, and it seems working.

But any existing other solutions?

Thanks.