Steps to replicate the issue (include links if applicable):

Navigate to https://en.wikipedia.org/wiki/Special:AbuseLog/34250998

Try this in your browser console:

>> mw.config.get('wgAbuseFilterVariables').user_mobile
true

>> (await $.get("https://en.wikipedia.org/w/api.php?action=query&list=abuselog&afllogid=34250998&aflprop=details&format=json")).query.abuselog[0].details.user_mobile
""

What happens?:

As shown, the web interface is correctly showing user_mobile is true but the API is showing user_mobile is ""

What should have happened instead?:

user_mobile is true in both the API and web interface

Other information (browser name/version, screenshots, etc.):

The seems to be a regression; I've been working on a script for client-side filter testing, and it stopped working sometime in the last few weeks.