Troubleshoot XMLRPC Sync pfBlockerNG 3.0

[paddyboyfloyd]

I've got about 10 pfSense boxes that I manage and I'm running pfBlocker on all. Box A is the master and I sync the configuration to the 9 other boxes. The 9 boxes are all configured basically the same, but 1 of the 9 is failing to sync the pfBlockerNG configuration. The only error I'm seeing in the pfblockerNG log is

Sync with [ https://192.168.5.1:443 ] ... Failed!

I get the following alert in the master pfSense:
A communications error occurred while attempting to call XMLRPC method merge_installedpackages_section: @ 2021-05-05 16:45:07

No indication of error or anything on the child pfSense. I've reentered the credentials three times, so I don't believe that it's a simple authnetication failure.

I see the traffic being passed over my OpenVPN interface on the child pfSense, but it's not syncing the configuration.

I'm clueless as to where I could look next to further troubleshoot this?

Thanks!

[RonpfS]

@paddyboyfloyd Are all boxes running the same pfSense version ?
Search Results for merge_installedpackages_section

[paddyboyfloyd]

@ronpfs The Master is running 2.5.1 and all the child boxes were running 2.4.5. I upgraded the child pfsense that's failing to the same version as the master, but I'm still getting the

/usr/local/www/pfblockerng/pfblockerng.php: New alert found: A communications error occurred while attempting to call XMLRPC method merge_installedpackages_section:

error when I force a reload on the master.