Thanks for reporting this Jeff. For about 10 days this bug was making me crazy... this is what I encountered in the process.

- My sites at Godaddy shared hosting with php 5.6 had no problems, so as my test sites at poopy.life.

- On my development localhosts using Ampps php 7.1, the server was crashing at least once every minute or, so, and almost immediately after visiting the theme Customizer. Downgrading the php to 5.6 helped a bit, but did not solve the whole issue, but the sites slowed down a lot. After deleting Ampps and Re installing it in a different folder, things did NOT get any better. I must have installed a WP site 50 times with different settings and plugins with no avail. Mind you that this was happening on all 3 Windows 7 computers that I was using. As a theme and plugin developer I started questioning if any of my code was causing the issue, which I had to really comb things for hours, almost line after line looking for clues...

- Finally, I gave up on Ampps, and installed Xampp, which solved all the crashing issues. Xampp comes with php 7.2 which of course comes with the not countable warning, and I guess that warning in the future will be upgraded to an error message. Thankfully the fix for that warning was an easy one for my themes, and life was good again.

On Tuesday, when the WP 4.9.8 beta1 came out along with the news of the memory leaks in WP, I was relieved... 10 days to hell and back, but I learned a lot in the process, like cursing at your computers, things don't get fixed magically ! I got the beta 2 yesterday, but I still did not test it for memory leaks on my Ampps installations yet, that's next on my agenda I guess !

Thanks again Jeff.