Steps to reproduce the issue

To redirect non-existing urls on my Joomla sites to a logical, existing url on my site I use (like many) the redirects plugin.
It worked fine until a while ago.
Today I got a notification from google that some pages are not available.
When you go to the url you get a (joomla) orange screen with an error message: Sorry, there was a problem we could not fix.
The server returned a "500 - Whoops, looks like something went wrong."

Expected result

Redirect to correct page / url on site...
When I look up the url in the redirects list it is in there and the referring url is correct.....
Removing the url from the list results in a 404-error page as you would expect.

Actual result

After adding the url again with a url of an existing page on the site the orange error page appears again.

Expired url: https://htm63.com/av-t-en-francais/contactez-av-transaction
new url : https://www.htm63.com/en-francais/contactez-moi

I have looked at and tried everything, but I can't get it to work.... Who knows how to get it to work again?

System information (as much as possible)

System:
Setting Value
PHP Built On Linux dh29280.eatserver.nl 3.10.0-962.3.2.lve1.5.61.el7.x86_64 #1 SMP Wed Aug 18 07:50:15 UTC 2021 x86_64
Database Type mysql
Database Version 10.5.13-MariaDB
Database Collation utf8_general_ci
Database Connection Collation utf8mb4_general_ci
Database Connection Encryption None
Database Server Supports Connection Encryption No
PHP Version 7.4.27
Web Server Apache
WebServer to PHP Interface cgi-fcgi
Joomla! Version Joomla! 4.0.6 Stable [ Furaha ] 15-January-2022 17:06 GMT
User Agent Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.99 Safari/537.36

PHP:
Setting Value
Upload Max Filesize 32M
Post Max Size 32M
Memory Limit 128M
Open basedir /var/www/vhosts/htm63.com/:/tmp/
Display Errors Off
Short Open Tags On
File Uploads On
Output Buffering On
Session Save Path /var/lib/php/session
Session Auto Start 0
XML Enabled Yes
Zlib Enabled Yes
Native ZIP Enabled Yes
Disabled Functions opcache_get_status
Multibyte String (mbstring) Enabled Yes
GD Available Yes
iconv Available Yes
intl Available Yes
Maximum Input Variables 1000

Config file:
Setting Value
offline false
offline_message Deze site is niet beschikbaar wegens onderhoud.
Probeer het later nog eens.
display_offline_message 1
offline_image
sitename iad France - Région d'Ambert - Livradois-Forez
editor jce
captcha recaptcha_invisible
list_limit 20
access 1
debug false
debug_lang false
debug_lang_const true
dbtype mysqli
host xxxxxx
user xxxxxx
password xxxxxx
db htmu
dbprefix htm4_
dbencryption 0
dbsslverifyservercert false
dbsslkey
dbsslcert
dbsslca
dbsslcipher
force_ssl 2
live_site
secret xxxxxx
gzip false
error_reporting default
helpurl https://help.joomla.org/proxy?keyref=Help{major}{minor}:{keyref}&lang={langcode}
offset UTC
mailonline true
mailer mail
mailfrom hans@htm63.com
fromname IAD Region Ambert Livradois-Forez France (HTM)
sendmail /usr/sbin/sendmail
smtpauth false
smtpuser xxxxxx
smtppass xxxxxx
smtphost localhost
smtpsecure none
smtpport 25
caching 0
cache_handler file
cachetime 15
cache_platformprefix false
MetaDesc Site de Hans KETTING pour iad France (Auvergne, france), Conseiller en immobilier avec des maisons dans la région d'Ambert (63600) dans le Livrados-Forez
MetaAuthor true
MetaVersion true
robots
sef true
sef_rewrite true
sef_suffix true
unicodeslugs true
feed_limit 10
feed_email none
log_path /var/www/vhosts/htm63.com/httpdocs/administrator/logs
tmp_path /var/www/vhosts/htm63.com/httpdocs/tmp
lifetime 15
session_handler database
shared_session false
session_metadata true
memcached_persist true
memcached_compress false
memcached_server_host localhost
memcached_server_port 11211
redis_persist true
redis_server_host localhost
redis_server_port 6379
redis_server_db 0
cors false
cors_allow_origin *
cors_allow_headers Content-Type,X-Joomla-Token
cors_allow_methods
behind_loadbalancer false
proxy_enable false
proxy_host
proxy_port
proxy_user xxxxxx
massmailoff false
replyto
replytoname
MetaRights (C) - 2021 - Hans KETTING
sitename_pagetitles 2
session_filesystem_path
session_memcached_server_host localhost
session_memcached_server_port 11211
session_redis_persist 1
session_redis_server_host localhost
session_redis_server_port 6379
session_redis_server_db 0
frontediting 1
block_floc 1
log_everything 0
log_deprecated 0
log_priorities all
log_categories
log_category_mode 0
cookie_domain
cookie_path
asset_id 1
redis_server_auth xxxxxx
session_redis_server_auth xxxxxx
ftp_user xxxxxx
ftp_pass xxxxxx
proxy_pass xxxxxx

Additional comments