There are some points you need to do.
Please don’t execute check plugins on the command line as root.
Do this every time as the site user. Also your curl test should be done as site user to have the same environment as the check plugin.
What happens if you try the “check_form_submit” on the CLI with the following options?
~/lib/nagios/plugins/check_form_submit -I www.xxx.nn -u /login -p 443 -s -e adresa -d
Also you should check what this server really gives as an response with
openssl s_client -connect www.xxx.nn:443