So I’ve noticed something a bit odd.
Muting a topic works as intended on my pc. So far so good. However, on my mobile browser the topics are still visible under their respective categories on the forum’s front page. If you go into a particular category, the muted topics are once again properly invisible.
It’s not the end of the world, but it does clutter up a bit of real estate. 
Try checking out the setting page in your mobile. Maybe the setting is set up per browser basis.
IIRC Muted topics aren’t invisible, you just don’t get notifications for them anymore.
That’s not been my experience at all. Allow me to illustrate through the magic of screenshots, using my own topic as a mute/unmute guinea pig.
PC browser (Firefox). In the meta category, with my topic unmuted. Witness its glory.
PC browser. In the meta category, with my topic muted. Poof! Gone!
Mobile browser. Forum front page in category view, with my topic muted. …and yet it’s visible.
Mobile browser. Inside the meta category, with my topic muted. Poof 2: The Poofening.
My issue is this: Real estate is limited on a mobile screen, so if a muted topic shows up on the front page, it’s edged out at least one topic that might have been of more interest than the one I explicitly had no interest in. Though like I said: it’s not the end of the world, and certainly nothing I would ever go to the barricades for. Just an oddity I noticed.
ETA: I’ve used different defaults for the forum front page (category, latest, etc.) with the same end result.
