Ok, I installed all PHP-FPM, each one at time, and selected the webserver, following the procedure at <http://wiki.centos-webpanel.com/webservers-update>, and this seems solved the problem.
I could not find any information about install PHP-FPM once at time. It was executed, but it is installed just the prerequisites to PHP, not the PHP-FPM.
This information could added that page.
Seems was wiped out all old earlier PHP versions, except 7.1, and an old 4.4 I had installed before. That processes remains in memory, so the panel was trying to execute that old PHP4.4 version, bringing the error in logs:
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2018/12/03 16:54:09 [error] 25422#0: *8994 FastCGI sent in stderr: "PHP Fatal error: <br>The file <b>/usr/local/cwpsrv/htdocs/admin/admin/loader.php</b> was encoded with the PHP 5.6 ionCube Encoder and requires PHP 5.6 or PHP 7.0 to be installed. in Unknown on line 0" while reading response header from upstream, client: 12.23.34.45, server: localhost, request: "GET /admin/loader.php?func=get_load&_=1543788552450 HTTP/1.1", upstream: "fastcgi://unix:/usr/local/cwp/php71/var/sockets/cwpsrv.sock:", host: "panel.domain.com:2031", referrer: "
https://panel.domain.com:2031/admin/index.php?module=php_selector3"
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And bringing the panel completely down.
After reboot the server, it is working now.
Thanks.