did you already try this?:
We’re not on Ubuntu 18.04 yet and still running 16.04. But every time we update the OS by apt-get (doesn’t matter if upgrade or dist-upgrade) and it contains a SQL update the things described in the link above needs to be done.
If that solves your problem and you have some sort of automatic updates turned on you could think about to deactivate them and run them regularly by yourself.
If that doesn’t solve your problem maybe someone else has another idea.