Having issues as well with 3 Logitech 4K's in OBS.
On my Intel mac in Big Sur, they could all feed in, in realtime to OBS, Now on my Intel 16in i9 MBP, and 16in M1 Pro, they are very delayed at 4K, OBS reports no issues with framerates, but the cameras are unusable unless I drop them all down to 1080p, sometimes I can get one up to 1440 24p.
They're fine with 1 connected, or even 2, but when there's 3 it all goes crazy.
This all worked fine in Big Sur.
Noticed where there used to be 3 options in Big Sur, for how the signal is compressed/sent from the cameras, now there is only one (NV12 422), unless I go below 1080, then I get YUV 422 as an option as well.
Have tried the Intel and Apple Silicon builds of OBS (Intel build on both Intel and M1 Pro machines), problem is the same, though M1 is a bit smoother at times, I think.
Plugging them into a hub or directly to the machine makes zero difference.
Seems to be something changed in Monterey, and it sucks for my work :/