We updated our Vigor3912 to firmware 4.4.3.2 in January 2025…

Shortly afterwards, we noticed strange behaviour with certain software and websites running from or accessed from, the client machines on the LAN behind the 3912. 
The same client machines would not exhibit the same behaviour when not on the network behind the 3912.

We initially assumed the issue to be with Windows 11 24h2, or one of the many ancillary patches that pulled in, which we’d also recently updated all of the client machines to.  But after rolling back a couple of machines to Windows 11 23h2, found that not to be the case.  We even looked at the locally installed anti-virus/firewall solutions as a culprit, but found them not to be the cause either.

The specific issues were –
1.      For a specialist Actuarial Tool, the tool would take circa 3 to 5 Minutes to load, once loaded no other issues found.
2.      Endpoint Patch Management/Remote Access tool – all endpoints became inaccessible, when behind the 3912, even from another machine also behind the 3912.
3.      The Office 365 Configuration Management Webpage ( https://config.office.com ), became inaccessible – timed out on connection attempts.
4.      Various other websites, (all https based) – timed out on connection attempts, but not all https based websites exhibited this behaviour.

We ultimately rolled back the firmware on the 3912 to 4.3.6.2 and all of these issues vanished. 

Looking further into the affected software and websites all failed with access timeouts, whilst performing SSL based verification/logon's to resources on the internet, via the standard port 443.
 

Interesting post.
I bought a 3912s and it came with 4.4.3.2; when doing a little tyre kicking, it all seemed ok but I moved my AP906 devices (which were working fine on my 2860) to the 3912s and things (generally) don't work. From using a wireless device where I struggle to get to many sites, using a VPN (NordVPN), I can do all I need to, but that doesn't help with devices such as Sonos,solar panels etc. I suppose I could route everything through NordVPN (that's only just occurred to me) but that seems inelegant at best.
I raised a support ticket a few days ago but nothing back yet.

I may try doing what you did tho the only listed firmware for my device is 4.4.3.2; that said, on the FTP site, there is only a folder for 3912 so I assume that includes the 3912s. My only concern is that someone said they'd opened their 3912 and it had no space for an SSD so it's not *exactly* the same hardware.
Did you just backup config (as a precaution) etc. then apply the older firmware or did you need to apply configuration again?

Oh, i did note that 4.4.3.2 is marked as a critical release; did eschewing that not worry you?  did you report this issue to Draytek?  I previously had a problem with AP906 firmware and was told to downgrade (thus not applying the critical fixed) and the support engineer (who I think in fairness is one of the more junior engineers) didn't seem bothered by that.

Thanks

I downgraded to 4.3.6.2 and things started working.
VigorConnect says firmware not supported but so far that is the only issue seen.
I contacted DrayTek support asking for a working version of firmware with the latest critical fixes but not got reply yet.
In a corp environment (where one would require supported firmware) the 3912s is not a viable product atm as far as I can tell. It’ll be a blinder when it’s got working supported firmware tho.