please see details in attached template. 3 external Dell P2419HC monitors. Monitors 1 and 2 work on USB-C. Monitor 3 is connected via HDMI due to bandwith limitations of USB-C. Monitor 3 will not be detected when USB-C monitors 1 and 2 are on; but will be if I turn off Monitor 1. This was working fine for a week. I disconnected my lap top to work remote. when I returned and plugged it back in, it stopped working as described. Please see attachment for more details.
The Intel HD Graphics engines will only support 3 monitors simultaneously. From everything that I can see, you have 4 connected. Only 3 can work at any point in time. This is exactly what I expect and what you are seeing.
If you want the three external monitors to work, you must disable the laptop's built-in monitor. You need to make sure that this is happening (automatically) when you close the lid. I have seen cases there this did not always happen (and this was also with a Lenovo laptop).
I will also point out that if you are sticking to three standard 1080p@60Hz monitors, there is plenty of bandwidth in the DisplayPort channel that is embedded in the USB-C connector to support three daisy-chained (or MST Hub-based) monitors.