URGENT: USG110 fw 4.65(AAPH.1) - Slow downloads / timeouts on certain sites

Recently we started having issues downloading updates from Dell using their Dell Command Update app on Windows. It used to take a minute or so on our 500 Mbit connection, and now it takes hours. I also noticed that trying to download a Verizon One Talk Windows app setup is the same, it sits there and takes forever and eventually times out.

One Talk Downloads page (verizonwireless.com)

I took a laptop home and tested it and downloads for both are fast as expected, using the same ISP at home as we use at my Office. So I tried disconnecting our USG110 in the office and connecting a laptop directly to the cable modem and it works fast as expected.

I have tried disabling IDP, ADP, BWM, AntiVirus and everything else I could think of and these sites are still slow and time out. This happens on different model PCs. The only thing that has changed is that this was not an issue until upgrading to the recent firmware release for security fixes. I am afraid to roll back the firmware because I don't want to lose the security fixes.

I also tried different public DNS server (google, cloudflare, opendns) and none of them made a difference.

Please help, we need to be able to download security/stability updates from Dell and important our phone system app from Verizon.