You could try making sure the stick is fully up to date.
Worst case set it back to factory settings
Although considering Sky Showcase is a cominbation of other channels and has no on demand content are you overly fussed about it being in SD? As the content will most likely be on another Sky branded channel.
I mentioned on my previous post on this thread that i am not seeing the HD on the end of the Sky Showcase live channel information on none of the playback devices that i have currently checked with my Boost Membership.
The playback devices not showing the HD on the end of the Sky Showcase channel from the Entertainment Now & Next TV Guide for me is my Youview Box NOW App and my NOW 4K Smart Box.
Though Sky Max the second new channel added is showing HD in the channel name.
Even though it's not showing HD on the end of the channel name to my eyes it definitely 1080p HD with a streaming quality figure of around 7800.
I would thought all NOW needs to do is add HD on the end of the Sky Showcase channel information name and don't need to upgrade the picture streaming quality.