job has started, but not responded for 10 seconds

Hello,

brand new WP install in Docker on top of nginx and with PHP-FPM 8.1 . There are no other plugins installed, I just installed BackWPUp and configured a simple backup to folder job.

When I run the job, I get the famous “job has started, but not responded for 10 seconds”.
I tried to set the WP_ALTERNATE_CRON to true but then : running the job manually shows a blank page – and refreshing the page manually shows me a currently running job, for which the logs show it actually finished to create the archive.
So : absolutely not reliable.

Can you help me sort out what’s going wrong ?

As required, here are the “Information” tab data :

WordPress version	6.5.5
BackWPup version	4.1.3 Get pro.
PHP version	8.1.29 (64bit)
MySQL version	11.4.2-MariaDB-ubu2404
cURL version	8.7.1
cURL SSL version	OpenSSL/3.3.1
WP-Cron url	https://<redacted>/wp-cron.php
Server self connect	Not expected HTTP response:Status-Code: 200
Server: nginx
Date: Sun, 14 Jul 2024 00:22:30 GMT
Content-type: text/html; charset=UTF-8
X-powered-by: PHP/8.1.29
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Cache-control: no-cache, must-revalidate, max-age=0
Strict-transport-security: max-age=15768000; includeSubdomains; preload
Document root	/var/www/html
Temp folder	/var/www/html/wp-content/uploads/backwpup/bd31b4/temp/
Log folder	/var/www/html/wp-content/uploads/backwpup/bd31b4/logs/
Server	nginx/1.27.0
Operating System	Linux
PHP SAPI	fpm-fcgi
Current PHP user	www-data
Maximum execution time	30 seconds
BackWPup maximum script execution time	30 seconds
Alternative WP Cron	Off
Disabled WP Cron	Off
CHMOD Dir	0755
Server Time	0:22
Blog Time	00:22
Blog Timezone	
Blog Time offset	0 hours
Blog language	en-US
MySQL Client encoding	utf8
PHP Memory limit	256M
WP memory limit	40M
WP maximum memory limit	256M
Memory in use	6.00 MB
Loaded PHP Extensions:	Core, PDO, Phar, Reflection, SPL, SimpleXML, Zend OPcache, bcmath, cgi-fcgi, ctype, curl, date, dom, exif, fileinfo, filter, ftp, gd, hash, iconv, imagick, intl, json, libxml, mbstring, mysqli, mysqlnd, openssl, pcre, pdo_sqlite, posix, readline, session, sodium, sqlite3, standard, tokenizer, xml, xmlreader, xmlwriter, zip, zlib

Thanks for your help !!!