External monitors show blank screen until restart
The video signal on the  Thunderbolt connection on your MBP is actually Display Port so you are actually going from Display Port to HDMI.  I am not a fan of converting signals because it's flaky at best.

If you must connect to HDMI, try an active1 adapter like the TRENDnet USB-C to HDMI 4K.  They have two versions - one that does 30Hz and another that does 60Hz (it's the Power Delivery version).

What is preferable, is to go from USB-C to Display Port which is actually Display Port to Display Port, so no there's conversion involved.  No conversion means less points of failure.    

jksoegaard's comments provides more evidence of this:


  Just to add a real-life experience: I'm using 2 USB-C to DisplayPort adapters (which are basically similar to the HDMI adapters) - and this works without any problems in that regard. Several times a week I plugin in both monitors after the MacBook Pro is booted (basically I never turn it off) - removing the cables again also never give problems



1 I wrote an answer on this very topic:  Passive vs. Active Adapter