I tried installing the x86 version of QMono 4.6 on my QNAP which doesn’t require FW 4.3. However Sonarr just crashes with that version. The refreshseries task crashes at some point so Sonarr would only stay up for about a minute.
I removed 4.6 and went back to QMono 4.4.2 x64, and Sonarr is working again. I’d suggest not upgrading at this point if your Sonarr is working ok, and just ignore the health alert.