This is the latest W2100 Professional GPU driver from AMD Support: Workstation .
Is this the same as a MST - Mini DP / Hub?
Are you using AMD Eyefinity to see if it see all three monitors?
According to this website, the W2100 only supports two monitors: Max Monitors SAPPHIRE AMD FirePro W2100? [SOLVED] - The World's Best PC Builder .
Maximum Monitors On The SAPPHIRE AMD FirePro W2100? (100-505821)
- Q: How many monitors can I connect on the SAPPHIRE AMD FirePro W2100 (100-505821)?
- A: You can connect up to 2 monitors on the SAPPHIRE AMD FirePro W2100.
NOTE: the number of outputs on a video card is not an indicator of the number of monitors you can connect to it. Video cards with only 2 outputs might connect 8 monitors (ex: if it has 2 DisplayPort 1.2 MST outputs, you can daisy chain 4 monitors on each output) while one with 6 output might only allow a maximum of 4 monitors (video card limitation).
Yes, the U2415 monitor acts as an MST hub.
Eyefinity only sees two monitors.
I keep thinking its a bug in Windows 10 display settings, my next step might be to reinstall Windows 10.
If you decide to reinstall Windows 10, do an "Ingrade Repair" instead. That way you won't lose any of your installed 3rd party apps and drivers. Windows 10 is installed like it had be upgraded from Windows 7.
Ingrade Repair is basically running the Windows version 1803 installation while on Windows Desktop. When it finishes, you can use Windows Cleanup feature on the C drive to remove the Windows.old installation if you want to clear up space. You can upgrade via USB or DVD.
Did Windows recognize all three in the past or never did? If it never did, then it might be either the Hub or cable to the hub is not compatible especially if you are using an adapter.
fsadough would probably be the person to advice you since you are using a Professional AMD GPU Card. He might be able to make suggestions to get the third monitor working in Windows and Eyefinity.
need more accurate info, how the monitors are connected to W2100