Comment 1 for bug 1888184

Thanks for taking the time to report this bug and trying to make Ubuntu better.

I've seen some people facing issues regarding the packet version compatibility, you have version 3 and 4 in your setup. I tried to make a quick research about any compatibility issue between version 3 and 4 but I did not find something useful. I found a recent post on the nagios support forum but I do not have permission to access it, from its short description I got that "agents are falling back to packet version 2 when query an agent in version 4 by a plugin in version 3". This seems to match your case and it might be an upstream issue. It'd be great if you could engage in a discussion about it with upstream. In case you do that please link it here.

Since you described it is still working, you can try to follow one of the solutions described in this article to silence those errors for now:

https://support.nagios.com/kb/article/nrpe-remote-does-not-support-version-3-packets-786.html