Can't connect to QNAP NAS

[James Blonde]

Been having problems since a recent  (last 3-4 days) Avast and Windows 10 update.  I can no longer connect to my QNAP NAS using QFinder and it doesn't appear in my network list.  It does seem to appear in the Qfinder server list at boot up, but can't connect on Qfinder when I try, and when I refresh the server list, it vanishes. 

I can connect to it on my phone using QManager (all seems to be working fine) and it appears on my list of Plex servers in Plex and is fully accessible. 

Both PCs are up to date with Avast and Windows updates (Windows 10 Pro), I've tried repairing my Avast Premium Security installation and my Network is trusted in Avast on both PCs I use on my network. 

Any suggestions??  Been like it for a few days now.  This has happed literally just at the point where I was going to try to do more than file sharing and media server work on my NAS

[James Blonde]

FWIW, I'm now thinking this is a NAS issue rather than PC / Network / Avast.  I've disabled the QuFirewall on the NAS(!) and can connect again.  No idea what changed on QuFirewall or why it stopped working, as I didn't make any changes to that on the NAS, so maybe it's all unconnected and maybe all these updates are coincidental?  Or maybe it's still somehow connected?  Urgh!