What does this unbound log mean?

[verfluchten]

T11:04:44       unbound[60940]   [60940:0] notice: remote address is xx.yy.zz.tt port 53   
T11:04:44       unbound[60940]   [60940:0] notice: send failed: No buffer space available   
T11:04:44       unbound[60940]   [60940:1] notice: remote address is xx.yy.zz.tt port 53   
T11:04:44       unbound[60940]   [60940:1] notice: send failed: No buffer space available

[EricPerl]

Realtek NIC?
https://forums.freebsd.org/threads/send-failed-no-buffer-space-available.92170/

[EricPerl]

A cursory search also indicates traffic shaping could be a cause. Do you use that?

[verfluchten]

I wasn't really wondering what is causing this. I am more interested in the consequences: what is not working?

[EricPerl]

I would think you're in a better position to answer this than I/we are...
I would suspect a failure to resolve, possibly solved via retry.