Apache 2.4 suddently dies in a fresh ubuntu 18.04. Certbot installed. Certificates authorized manually and installed manually (certbot did not touch my files). The logs are these:

/var/log/apache2# cat error.log.1
[Mon Apr 08 14:00:59.183891 2019] [macro:warn] [pid 26822] AH02800: macro 'hellotrip' (defined on line 1 of "/etc/apache2/sites-enabled/500-hellotrip.conf"): argument '$dummy' (#1) never used
[Mon Apr 08 14:00:59.256064 2019] [core:warn] [pid 26829] AH00098: pid file /var/run/apache2/apache2.pid overwritten -- Unclean shutdown of previous Apache run?
[Mon Apr 08 14:00:59.259749 2019] [mpm_prefork:notice] [pid 26829] AH00163: Apache/2.4.29 (Ubuntu) OpenSSL/1.1.0g configured -- resuming normal operations
[Mon Apr 08 14:00:59.259974 2019] [core:notice] [pid 26829] AH00094: Command line: '/usr/sbin/apache2'
[Mon Apr 08 17:21:56.130758 2019] [mpm_prefork:emerg] [pid 26833] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Apr 08 17:21:56.132054 2019] [mpm_prefork:emerg] [pid 26834] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Apr 08 17:21:56.136360 2019] [mpm_prefork:emerg] [pid 26840] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Apr 08 17:21:56.136558 2019] [mpm_prefork:emerg] [pid 26843] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Apr 08 17:21:56.136843 2019] [mpm_prefork:emerg] [pid 26835] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Apr 08 17:21:56.137147 2019] [mpm_prefork:emerg] [pid 26832] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Apr 08 17:21:56.137359 2019] [mpm_prefork:emerg] [pid 26836] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Apr 08 17:21:56.833216 2019] [core:alert] [pid 26829] AH00050: Child 26832 returned a Fatal error... Apache is exiting!
[Mon Apr 08 17:21:56.833273 2019] [:emerg] [pid 26829] AH02818: MPM run failed, exiting
/var/log/apache2#

This is my version:

/var/log/apache2# apache2ctl -V
[Tue Apr 09 22:17:03.105574 2019] [macro:warn] [pid 7155] AH02800: macro 'hellotrip' (defined on line 1 of "/etc/apache2/sites-enabled/500-hellotrip.conf"): argument '$dummy' (#1) never used
Server version: Apache/2.4.29 (Ubuntu)
Server built: 2019-04-03T13:22:37
Server's Module Magic Number: 20120211:68
Server loaded: APR 1.6.3, APR-UTIL 1.6.1
Compiled using: APR 1.6.3, APR-UTIL 1.6.1
Architecture: 64-bit
Server MPM: prefork
 threaded: no
 forked: yes (variable process count)
Server compiled with....
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
 -D APR_USE_SYSVSEM_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D DYNAMIC_MODULE_LIMIT=256
 -D HTTPD_ROOT="/etc/apache2"
 -D SUEXEC_BIN="/usr/lib/apache2/suexec"
 -D DEFAULT_PIDLOG="/var/run/apache2.pid"
 -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D AP_TYPES_CONFIG_FILE="mime.types"
 -D SERVER_CONFIG_FILE="apache2.conf"

In fact, there are plenty of forums that suggest changing the Mutex mechanism in the configuration. For example this one:

https://stackoverflow.com/questions/50652808/apache-shutdown-couldnt-grab-mutex

But before applying any magic I want to:

a) Understand what file apache is trying to lock.
b) eventually force to repeat the error (I want you apache to do it now) so I can provoke de crash.

Question:

How can I know what file is apache willing to lock when it says "couldn't grab the accept mutex"?