Could you please confirm that you are daisy-chaining both monitors via the Type-C connector.
Can you also provide me with the model of the monitores?
I have an adapter from Thunderbolt 3 to Thunderbolt 2. I'm beginning to suspect it's either an issue with Windows or Intel drivers because I tried from a clean install of Windows 10 on a late 2012 MacBook Pro retina and it exhibits the same exact symptoms. The MBP also has an Intel graphics chip. I tried plugging the extra monitor directly into the Mini DisplayPort but this does not work at all, I don't think it's supposed to however from what I can glean from Apple Support (my machine becomes unresponsive for about 15 seconds when I do this and then nothing).
I have definitely installed all the latest drivers, the latest Thunderbolt firmware, and the latest BIOS.
I'll have to do some research into the model of the displays as I don't see them anywhere physically.
I did some more digging and officially only one monitor is supported off the Thunderbolt connector; however we know that it works up to two monitors but only at 1080p and it is very possible that these two monitors that you have are higher resolution than 1080p.
Have you tried running one monitor of the DP port? This could be a solution for your configuration.
The other concern I have is that perhaps the adapter is being recognized as a third device and if that is the case, three display devices wont work daisy-chained but this is something I wont be able to test unfortunately and I cannot confirm.
I hope this helps,