Since the switch to custom tags instead of predefined ones, it seems like the “Get Stream Tags” endpoint is only returning automatically added tags (or tags that had been set before the switchover).
Is there a plan to address this with an update to the endpoint (Or the “Get Streams” endpoint, just adding a Tags field)?
There should be an announcement about it on the forums and/or social media (@TwitchDev on Twitter) and/or the Documetnation change log when this occurs Changelog | Twitch Developers