Apache2 is looping because of timthumb file

Question

I have an apache2 server setup with the following .htaccess file at /

<IfModule mod_rewrite.c>
<IfModule mod_env.c>
  SetEnv HTTP_MOD_REWRITE On
  </IfModule>

  RewriteEngine on

  #REDIRE HTTPS
  #RewriteCond %{HTTPS} off
  #RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R,L]
  #REDIR WWW
  #RewriteCond %{HTTP_HOST} !^www\.
  #RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L,QSA]

  #resize photos
  RewriteRule ^photos_(\d*?)x(\d*?)\/(.*)(.jpg|.jpeg|.png|.gif)$ %{ENV:REWRITEBASE}/lib/timthumb/timthumb.php?src=/photos/$3$4&w=$1&h=$2&zc=1 [NC,L]

  #RewriteRule ^photos_ext_(\d*?)x(\d*?)\/http([s]*).*?\/(.*)(.jpg|.jpeg|.png|.gif)$ %{ENV:REWRITEBASE}/lib/timthumb/timthumb.php?src=http$3://$4$5&w=$1&h=$2&zc=1 [NC,L]
  #RewriteRule ^photos_ext_(\d*?)\/http([s]*).*?\/(.*)(.jpg|.jpeg|.png|.gif)$ %{ENV:REWRITEBASE}/lib/timthumb/timthumb.php?src=http$2://$3$4&w=$1&h=$2&zc=1 [NC,L]

  RewriteRule ^photos_(\d*?)\/(.*)(.jpg|.jpeg|.png|.gif)$ %{ENV:REWRITEBASE}/lib/timthumb/timthumb.php?src=/photos/$2$3&w=$1&h=$1&zc=1 [NC,L]
  RewriteRule ^visuels_(\d*?)\/(.*)(.jpg|.jpeg|.png|.gif)$ %{ENV:REWRITEBASE}/lib/timthumb/timthumb.php?src=/visuels/$2$3&w=$1&h=$1&zc=1 [NC,L]


  #js traductions
  RewriteRule ^themes\/.*?\/js\/traduction.js$ %{ENV:REWRITEBASE}/traductionjs [NC,L,R=301]


  # Dispatcher
  RewriteCond %{REQUEST_FILENAME} -f [OR]
  RewriteCond %{REQUEST_FILENAME} -s [OR]
  RewriteCond %{REQUEST_FILENAME} -l [OR]
  RewriteCond %{REQUEST_FILENAME} -d
  RewriteRule ^.*$ - [NC,L]
  RewriteRule ^.*$ %{ENV:REWRITEBASE}index.php [NC,L]
</IfModule>


<IfModule mod_php5.c>
  php_value short_open_tag 1
</IfModule>

#<FilesMatch "\.(js)$">
#Header set Access-Control-Allow-Origin "*"
#</FilesMatch>


#optimisations
Options -Indexes
ServerSignature Off
SetOutputFilter DEFLATE
AddOutputFilterByType DEFLATE text/html text/css text/javascript application/javascript application/x-javascript font/ttf application/x-font-ttf font/otf application/x-font-otf font/opentype image/svg+xml application/x-httpd-php
#Pour les navigateurs incompatibles
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html
#les proxies doivent donner le bon contenu
Header append Vary User-Agent env=!dont-vary

<IfModule mod_headers.c>
  Header always set X-FRAME-OPTIONS "SAMEORIGIN"
  Header always set X-XSS-Protection "1; mode=block"
  Header always set X-Content-Type-Options "nosniff"
</IfModule>


<ifModule mod_php5.c>
  php_value zlib.output_compression 16386
  php_value zlib.output_compression_level 5
</ifModule>


FileETag none
<IfModule mod_headers.c>
  Header unset ETag
</IfModule>

<IfModule mod_expires.c>
ExpiresActive On
ExpiresDefault "access plus 1 week"
ExpiresByType image/gif "access plus 1 week"
ExpiresByType image/jpeg "access plus 1 week"
ExpiresByType image/png "access plus 1 week"
ExpiresByType image/x-icon "access plus 1 week"
ExpiresByType application/x-shockwave-flash "access plus 1 week"

ExpiresByType text/css "access plus 0 seconds"
ExpiresByType text/javascript "access plus 0 seconds"
ExpiresByType application/x-javascript "access plus 0 seconds"
</IfModule>



#No cache for DEV mode
<filesMatch "\.(js|css)$">
  FileETag None
  <ifModule mod_headers.c>
    Header unset ETag
    Header set Cache-Control "max-age=0, no-cache, no-store, must-revalidate"
    Header set Pragma "no-cache"
    Header set Expires "Wed, 11 Jan 1984 05:00:00 GMT"
  </ifModule>
</filesMatch>

and the following proxy pass in 000-default.conf

<VirtualHost *:*>
ProxyPreserveHost On

ProxyPass /wallet http://wallet/
ProxyPassReverse /wallet http://wallet/

ServerName localhost
</VirtualHost>

that proxies a docker application to from /wallet to http://wallet. When I now access an URL that looks like this http://localhost/series/adventure/adult/helloworld2 I get the following error after a while:

www_1         | [Thu Nov 01 16:02:49.226185 2018] [mpm_prefork:error] 
[pid 1] AH00161: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting
www_1         | localhost:80 127.0.0.1 - - [01/Nov/2018:16:02:47 +0000] "GET /lib/timthumb/timthumb.php?src=/photos/logo-default.jpg&w=300&h=300&zc=2 HTTP/1.0" 400 811 "-" "-"
www_1         | localhost:80 127.0.0.1 - - [01/Nov/2018:16:02:47 +0000] "GET /lib/timthumb/timthumb.php?src=/photos/logo-default.jpg&w=300&h=300&zc=2 HTTP/1.0" 400 811 "-" "-"
www_1         | localhost:80 127.0.0.1 - - [01/Nov/2018:16:02:47 +0000] "GET /lib/timthumb/timthumb.php?src=/photos/logo-default.jpg&w=300&h=300&zc=2 HTTP/1.0" 400 811 "-" "-"
www_1         | localhost:80 127.0.0.1 - - [01/Nov/2018:16:02:47 +0000] "GET /lib/timthumb/timthumb.php?src=/photos/logo-default.jpg&w=300&h=300&zc=2 HTTP/1.0" 400 811 "-" "-"
this goes on forever

After that, the apache2 server is not accessible anymore and I need to restart it. I didn't find anything on the web but already tried to set mpm_event.conf and other parameters. Fundamentally I think there is a loop somewhere in my configurations. I can't figure out where though. I can post the docker file, but it's nothing special.

There are two lines that get called on startup of the php script:

define ('NOT_FOUND_IMAGE', 
"http://".$_SERVER["HTTP_HOST"].'/lib/timthumb/timthumb.php?src=/photos/'.$config["image_default"].'&w='.$_GET["w"].'&h='.$_GET["h"].'&zc=2');
define ('ERROR_IMAGE', "http://".$_SERVER["HTTP_HOST"].'/lib/timthumb/timthumb.php?src=/photos/'.$config["image_default"].'&w='.$_GET["w"].'&h='.$_GET["h"].'&zc=2');