Apache server sometimes gets stuck for minutes with requests getting backlogged and waiting too much to be processed

I've got a production server with **Apache 2.4.38** on **Debian 10** and sometimes the web server doesn't function properly and doesn't immediately send a response to the HTTP requests it gets (All virtual hosts requests on it are completely unresponsive (no matter what they reverse proxy to)). After a restart it immediately fixes itself or after being like this a while (seconds or even minutes) and starts sending A LOT of HTTP responses all of a sudden.

CPU and RAM usage seem to be fine, so it's definitely not that. I don't know what exactly is going on and why it's doing this. I've also changed mpm_event.conf settings, they currently are set to this:

StartServers                     2
        ServerLimit 100
        MinSpareThreads          25
        MaxSpareThreads          75
        ThreadLimit                      128
        ThreadsPerChild          25
        MaxRequestWorkers         400
        MaxConnectionsPerChild   5000

There are some errors I've seen in the Apache error log though:

[Tue Mar 22 19:53:38.339703 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 29595 still did not exit, sending a SIGKILL
[Tue Mar 22 19:53:38.339777 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 26190 still did not exit, sending a SIGKILL
[Tue Mar 22 19:53:38.339825 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 27903 still did not exit, sending a SIGKILL
[Tue Mar 22 19:53:38.339889 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 16907 still did not exit, sending a SIGKILL
[Tue Mar 22 19:53:38.339933 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 26880 still did not exit, sending a SIGKILL
[Tue Mar 22 19:53:38.340000 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 15384 still did not exit, sending a SIGKILL
[Tue Mar 22 19:53:38.340041 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 24971 still did not exit, sending a SIGKILL
[Tue Mar 22 19:53:38.340091 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 9780 still did not exit, sending a SIGKILL
[Tue Mar 22 19:53:38.340130 2022] [core:error] [pid 3375:tid 140244229465216] AH00046: child process 26317 still did not exit, sending a SIGKILL

What settings can I change that would fix this issue?