PostgreSQL 10 not archiving some WAL files

Hi

I have a strange case in some PostgreSQL instances that I monitor. First
the software versions and setup of a specific one:

- Windows Server 2012 Foundation
- PostgreSQL 10.10 x64
- archive_command = 'copy% p "D: \\ backup \\ wal \\% f" / y'

This setup worked very well for a long time, but since we upgraded
PostgreSQL to newer versions (10.x), sometimes it just skips archiving some
wal files. This seems to happen mainly when the server is shut down.
There's no messages about errors in the logs, and also no corresponding
.done file in archive_status, it just goes to the next wal file.

I would like to know if any of you had or has a problem like this, and if
you had, how you solved it.