I have an installation of Apache/2.4.18 running on Ubuntu 16.04. Apache is configured as Prefork MPM. PHP 7.0.22
Checking the error log at /var/log/apache2/error.log I see lots of these errors:
[Fri Jan 26 12:59:20.223248 2018] [core:notice] [pid 7203] AH00052: child pid 19370 exit signal Aborted (6)
[Fri Jan 26 13:39:20.475386 2018] [core:notice] [pid 7203] AH00052: child pid 24060 exit signal Aborted (6)
[Fri Jan 26 13:44:07.739520 2018] [core:notice] [pid 7203] AH00052: child pid 26568 exit signal Aborted (6)
[Fri Jan 26 13:44:17.748513 2018] [core:notice] [pid 7203] AH00052: child pid 6630 exit signal Aborted (6)
Other than these errors, the log is clean.
The available memory is not an issue, as I can see in top and free. Moreover, the current configuration of apache will not use more than 50% aprox. of the RAM available (other services included).
Googling around didn't provide any usable results. There is also this question but with no answer and apart from that it's not the same case as mine.
Apache is hosting some web sites, which don't seem to be affected by these errors.
Any ideas what the problem is and how it can be solved?