attempt to connect to Unix domain socket /var/lib/php5-fpm/web9.sock (*) failed

found similar problems here but do not solve
1) I have one server debian buster with ispconfig3.1 slave build following tutorial perfect server debian buster wit a typo3 web site running fine
2) I have a server in a similar testsystem slave build following tutorial perfect server debian stretch runing fine with a no longer existing typo3 site same typo3 version as above.
3) Did an inplace update to buster, went fine, added a new website for test, run fin with html. Started adding typo3 version as in 1) with same php optiones, just corrected the path to php log, (did the same procedure server times,always working.
Settings
<coode>
upload_max_filesize=10M
post_max_size=10M
memory_limit=256M
suhosin.request.max_varname_length=200
suhosin.post.max_name_length=200
suhosin.get.max_name_length=200
suhosin.get.max_value_length=2000
max_execution_time=300
suhosin.executor.include.whitelist=phar,vfs
always_populate_raw_post_data=-1
max_input_vars=1500
display_errors = On
error_log = /var/www/clients/client1/web9/private/php_error.log
</code>
got error
<code>
attempt to connect to Unix domain socket /var/lib/php5-fpm/web9.sock (*) failed
[Tue Feb 25 21:47:30.492776 2020] [proxy_fcgi:error] [pid 20355] [client 172.16.1.104:53023] AH01079: failed to make connection to backend: httpd-UDS
</code>
made php script for phpinfo(), running from command line. works fine, running from apache error as above
php --version
<code>
PHP 7.3.14-1~deb10u1 (cli) (built: Feb 16 2020 15:07:23) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.14, Copyright (c) 1998-2018 Zend Technologies
with Zend OPcache v7.3.14-1~deb10u1, Copyright (c) 1999-2018, by Zend Technologies
</code>
do you need any more information?
Thanks for help
Rainer