I just came to the forum to post this problem and saw this thread. I can't get a Raspberry Pi standalone web app to run if it is built in 2018r1 but it will run if it is built in 21017r3. I was about to download and try 2018r1.1 but it looks as though that won't help.
I do have libunwind installed.
pi@RPi3:~ $ apt list --installed libunw*
libunwind8/stable,now 1.1-4.1 armhf [installed,automatic]
What I'm finding is that the web app starts up ok but the moment I try to access it I just get the "Launching" message and the app's cpu jumps up to 100% and stays there.
Am I doing something stupid or is this a very serious bug?