Warning consistent with power event, but no power event occured

[ON2014]

This morning I was greeted with two emails from my qnap:

Date/Time: 07/28/2020 01:10:14 am
Level: Warning
The system was not shut down properly last time.

Date/Time: 07/28/2020 01:13:15 am
Level: Warning
[Mirror Disk Volume: Drive 1 2] The file system is not clean. It is suggested that you go to [Storage Manager] to run "Check File System".

These messages are typical of an unmanaged shut down (power failure). This is rare, however, since my qnap is on a UPS and, if such things do happen, I am greeted by a powered off unit—which was not the case today. No indications of a power failure were found anywhere else, either in my computer or household.

Any ideas what may have generated the warnings? Thanks.

[dolbyman]

are you sure the nas does not occasinally crash and reboot ?

[ON2014]

are you sure the nas does not occasinally crash and reboot ?

I've not seen it in 6+ years but I guess there's a first time for everything. Looking at the system log, I found "system started" between the warnings:

Warning 07/28/2020 01:13:14 AM System 127.0.0.1 localhost [Mirror Disk Volume: Drive 1 2] The file system is not clean. It is suggested that you go to [Storage Manager] to run "Check File System".

Information 07/28/2020 01:10:14 AM System 127.0.0.1 localhost System started.

Warning 07/28/2020 01:10:14 AM System 127.0.0.1 localhost The system was not shut down properly last time.

About an hour prior to this, a scheduled AV scan started but there was no notification that it completed.The scans normally take about 25 minutes. Is it likely the AV caused the crash?

[dolbyman]

I haven't had any such issues with my 3 QNAP NAS (419p+,853BU,951X) but there seems to be quite a few with spontaneous reboots

viewtopic.php?f=142&t=150707

If it only happened once so far, I wouldn;t worry too much

[ON2014]

I'll keep an eye on it. FWIW, my QTS is relegated to security updates only, so it isn't the newest version (4.3.3.1315).

Thanks.