I wasn't able to pinpoint the cause of error.
But it coincided with change of
- php from 7.1 to 7.3 and
- Joomla! from 3.9.6 to 3.9.8.
I have reverted to 3.9.6 and all seems good.
When I tried with 3.9.8 "just one more time", I had logging out issues i.e I couldn't.
I use an extension called Login as User but their changelog's do not suggest anything dramatic (I do not have latest version!!).
I probably create 20-30 articles a week, is that a lot? for me it is :)
All I can do is keep an eye on it and see what happens, so now I am:
- php from 7.3
- Joomla! 3.9.6
- Seblod 3.17.4
I will ask Siteground if they have info on hardware error, thanks :D