Multiple streams to YouTube and/or Facebook during a multi-court sporting event. Plenty of bandwidth (100 Mbps + for upload).

Every court goes to it's own stream on YT/FB/other host site - zero issues. All on laptops with i7's and Intel 40xx series graphics cards with vMix Basic

"Main Feed" pulls in court feeds for commentary - that feed's streaming to YT/FB is throttled, even at 720p/1.5 Mbps, even though 6 court feeds are all streaming fine at 1080p/3 Mbps at the same time.

Main feed is an i9, with 4060 series Intel GC, vMix Max (Pro subscription). CPU Mem is less than 20% while this is occurring.

If I stream to another host site outside YT/FB on the "main feed"; I can stream 1080p/6 Mbps with zero issues.

Has happened at two of my last three events after 3 years of zero issues; ended up using another "court" laptop with vMix Basic to push the Main Feed stream out to YT/FB with zero issues.

Possible something changed on the Main Feed laptop during a Windows Update, but what?

Thanks for any assistance.