[BUG] Channel Photos not loading (National Geographic Photos Channel)

Plex Web 2.12.6
PMS 1.3.3.3148
Ubuntu 14.04 (64-bit)
Chrome 55.0.2883.87 (64-bit)
FireFox 50.1.0 (64-bit)

Photos in channels do not load when selected in the Plex Web client (only present blank screen), but do work for other clients (i.e. Plex for Android).
Tested from the official Plex App store:

• NationalGeographic.bundle
• CatsPawImages.bundle
• AnnaKimPhotography.bundle
• Break.com.bundle

I opened up the developer tools, in chrome and firefox, and found the channels are stopping on the playQueues URLs (i.e. https://192-168-1-xx.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.plex.direct:32400/playQueues?X-Plex-Product=Plex%20Web&X-Plex-Version=2.12.6&X-Plex-Client-Identifier=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx&X-Plex-Platform=Chrome&X-Plex-Platform-Version=55.0&X-Plex-Device=Linux&X-Plex-Device-Name=Plex%20Web%20%28Chrome%29&X-Plex-Device-Screen-Resolution=1855x966%2C1920x1080&X-Plex-Token=xxxxxxxxxxxxxxxxxxxx) returning the following generic output:

<?xml version="1.0" encoding="UTF-8"?>
<MediaContainer size="3">
<PlayQueue id="1837" clientIdentifier="xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" totalItemsCount="1" type="movie" shuffled="0" />
<PlayQueue id="1885" clientIdentifier="xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" totalItemsCount="4" type="track" shuffled="0" />
<PlayQueue id="1882" clientIdentifier="xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" totalItemsCount="106" type="photo" shuffled="0" />
</MediaContainer>

(Redacted personal info.)

Any insight into this issue would be greatly appreciated. Am willing to help debug.