docspell-consumedir : doesn't match given pattern(s) Server: No files to upload

[RobertoFioravanti]

I've installed on my Qnap docspell following https://docspell.org/docs/install/docker/ . I upload a .pdf in /opt/docs/ folder

In docspell-consumedir I got this error

Got: /opt/docs/GREM/.@__thumb/<filename>.pdf.error
Skip '/opt/docs/GREM/.@__thumb/<filename>.pdf.error', doesn't match given pattern(s)
Server: No files to upload

What does it mean? Where can I specify the pattern(s)?

Thank you