[Flask] intermittent Internal Server Error on running flask site

[flaskee]

Hello all:

I'm just looking for pointers on where to check, in order to track this down.

The problem:

I have a production flask site,
on Apache /2.4.38; Debian 10.1, using a virtualized Python3.5/HTML5 site.

It works well! except that every few days it crashes with an Internal Server Error - 500.

When "crashed", the site itself is still loaded in Apache2,
as
nmap -A <my ip>
nmap -sP <my ip>
nmap -A <mydomain>
nmap -sP <mydomain>
all report the host is loaded;
and other static sites running on the same apache server still serve up just fine.

It does not *appear* to be a coding error,
as when it is running,
I have negotiated to each and every page in the site,
without causing a crash.

Still, randomly, the site fails.

I have been through:
* the web sites' error.log
* the web sites' acess.log
* /var/log/apache2/error.log
* /var/log/apache2/error.log.1
* /var/log/syslog
and I'm not finding the cause.

A
sudo systemctl stop apache2.service
sudo systemctl start apache2.service
gets the site running again.

Any tips on where else to check?

Thank you!

The Error
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator at webmaster at mydomain.org to inform them of the time this error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.

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