unbound error log of protocol not available

[Shunpei Shimokawa]

Hello,

The following error logs is detected irregularly on the operating DNS server.

Jan 11 12:14:33 unbound: [3965:a] error: recvfrom 361 failed: Protocol not available
Jan 11 12:34:22 unbound: [3965:a] error: recvfrom 403 failed: Protocol not available
Jan 11 13:00:18 unbound: [3965:a] error: recvfrom 562 failed: Protocol not available
Jan 11 14:35:22 unbound: [3965:a] error: recvfrom 421 failed: Protocol not available
Jan 11 14:35:23 unbound: [3965:a] error: recvfrom 544 failed: Protocol not available
Jan 11 15:38:37 unbound: [3965:a] error: recvfrom 524 failed: Protocol not available
Jan 11 17:14:19 unbound: [3965:7] error: recvfrom 536 failed: Protocol not available

There is no problem with the cache DNS status and it is not clear what is causing them.
Does anyone have any experience?
Please tell me how to investigate the details of the problem.

Thanks,