Problem solved !
I went to Site administration > Development > Debugging, and set "Debug messages" to "Developer". It was configured at "normal".
I had now details in the apache error log :
[Sat Sep 12 04:39:49.662733 2020] [php7:error] [pid 2151] [client ----------:49774] PHP Fatal error: cURL module must be enabled! in /var/www/moodle/lib/filelib.php on line 2873, referer: https://------.fr/question/question.php?returnurl=%2Fquestion%2Fedit.php%3Fcmid%3D4467&cmid=4467&id=33120
I fixed php-curl and CodeRunner is now working fine again !
Thank you very much for your help and your great plugin.