I’m having the same issue with CentOS 8. Suspecting an SELinux permissions issue, since SELinux has typically been the cause of my woes lately. I love security, but man SELinux can be a pain lol.
Edit for posterity (and google), my /var/log/php-fpm/www-error.log log file (it was taking 11GB of space on my machine and breaking Nextcloud):
[14-Aug-2020 13:39:06 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Connection refused) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[14-Aug-2020 13:39:06 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Connection refused) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[14-Aug-2020 13:39:06 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Connection refused) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[14-Aug-2020 13:39:06 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Connection refused) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[14-Aug-2020 13:39:06 UTC] PHP Warning: fsockopen(): unable to connec[14-Aug-2020 22:10:44 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Permission denied) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[14-Aug-2020 23:15:43 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Permission denied) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[15-Aug-2020 00:20:43 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Permission denied) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[15-Aug-2020 01:25:42 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Permission denied) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[15-Aug-2020 02:30:42 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Permission denied) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253
[15-Aug-2020 03:35:43 UTC] PHP Warning: fsockopen(): unable to connect to localhost:9982 (Permission denied) in /var/www/html/nextcloud/apps/richdocumentscode/proxy.php on line 253