NullPointerException and upload hangs using UI to upload 5G file to raw repository

Using Nexus 3.12.0-01 on Windows 2012, attempt a UI upload of a 5G file to a raw repository with Chrome and receive an invalid JSON error and NullPointerException in the UI. Using IE throws an "Arithmetic result exceeded 32 bits" which appears to be browser specific. The upload appears to hang.

Attempted the same upload on Nexus 3.12.0-01 on Mac and receive an Invalid JSON error and a 500 response in the request log:
127.0.0.1 - admin [31/May/2018:16:48:03 -0700] "POST /service/extdirect HTTP/1.1" 500 1854 30 "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36"

And the upload appears to hang.