Downgrade from 5291

Thanks for the detail

Would like to concentrate initially on why http://127.0.0.1:32400/web is not working. Would like to match what you had on the screenshot to the logs. What time was the 2nd screenshot which shows a black screen

could you get me the output from
sudo lsof -iTCP:32400
sudo lsof -iTCP:32401

I am not sure if this just lists PIDs or process names as well. If not, you can use
ps -ef
to get list of PIDs

Could I have that captured in terminal session on the mac from the failing 1.13.5.5291 and working 1.13.4.5271

I am not sure if sudo netstat -a -b -n gives us process names on Mac OS or not. If it does, please capture that into text file for both versions

I presume http://127.0.0.1:32400/web works OK on 1.13.4.5271

The logs show these network interfaces

Aug 08, 2018 19:31:43.335 [0x700001e39000] DEBUG - Network interfaces:
Aug 08, 2018 19:31:43.335 [0x700001e39000] DEBUG -  * 1 lo0 (127.0.0.1) (loopback: 1)
Aug 08, 2018 19:31:43.335 [0x700001e39000] DEBUG -  * 13 en0 (10.1.12.9) (loopback: 0)
Aug 08, 2018 19:31:43.335 [0x700001e39000] DEBUG -  * 19 vnic0 (10.211.55.2) (loopback: 0)
Aug 08, 2018 19:31:43.335 [0x700001e39000] DEBUG -  * 20 vnic1 (10.37.129.2) (loopback: 0)

So the IP I presume is 10.1.12.9
The vnic0 and vnic1 must be for the windows vm connection
Interfaces starting with v get ignored by Plex Media Server