I'm on 11.1 on a Mac Mini (latest Intel version) with 3 external displays. Two are connected via USB-C directly which means they are passively converting to DisplayPort. One is connected to HDMI from the Mac directly. All are 4k and all work fine.
That said, two of these displays were just purchased. They are kinda cheapo small "portable" displays (12.5" 4k native) which I primarily use for things like always visible terminal or slack/etc.
While experimenting with exactly how I wanted to connect these, I did for a time use Belkin's higher end USB-C to HDMI and had it misbehaving kind of randomly. After switching things around and connecting the one monitor with HDMI directly to the Mac I still had some issues... until I disabled FreeSync on the display itself and those issues disappeared.
The reality is that external displays have become extremely complex in the last few years with numerous optional functionalities such as HDR (which 100% always looks like garbage to me, I don't get the appeal) and VRR and so forth. Any issues I have experienced with external displays seem to have relationship with how complex the display's feature set is.
In this case, I wouldn't be surprised if the issue was linked to some subset of features that 11.1 breaks on now. I might suggest toggling such features off if possible on your displays to see if it helps anything.
That said, two of these displays were just purchased. They are kinda cheapo small "portable" displays (12.5" 4k native) which I primarily use for things like always visible terminal or slack/etc.
While experimenting with exactly how I wanted to connect these, I did for a time use Belkin's higher end USB-C to HDMI and had it misbehaving kind of randomly. After switching things around and connecting the one monitor with HDMI directly to the Mac I still had some issues... until I disabled FreeSync on the display itself and those issues disappeared.
The reality is that external displays have become extremely complex in the last few years with numerous optional functionalities such as HDR (which 100% always looks like garbage to me, I don't get the appeal) and VRR and so forth. Any issues I have experienced with external displays seem to have relationship with how complex the display's feature set is.
In this case, I wouldn't be surprised if the issue was linked to some subset of features that 11.1 breaks on now. I might suggest toggling such features off if possible on your displays to see if it helps anything.