The Apple USB-C HDMI adapter has a very non-intuitive behaviour that makes it difficult to work with.
Tested with LG 24MP88 LED monitor and Macbook Pro 2016 with MacOS High Sierra
Case 1: Display is turned off and then connected to the Mac via the adaptor. Even when the display is turned on, it does not detect until the adaptor is plugged in again.
Case 2: Turn off the display when it is connected to the Mac. The Mac still thinks that the display is connected and windows that are moved to the extended desktop are not visible.
Case 3: While using multiple monitors with separate HDMI adaptors, I have to plug them in the right order again if I want to retain the same configuration as when they were unplugged. If I plug Monitor 2 in first, then it gets detected as Monitor 1 and I have to change my display arrangement all over again.
Has anyone found a workaround for this? It seems like something Apple can easily solve by making their firmware a little smarter.