SOLVED! Turns out Qhrumphf was bang on. Thanks!
There was some cheeky hop residue clogging up the liquid post. Just had to do a brief unscrew/dissemble of the post to get at the clog.
I checked some other obvious stuff today. The keg is not frozen or empty. I also tried moving the liquid tube and disconnect onto another keg, and that's working just fine! So the good news is it's not a problem with the disconnect or anything above it. It's a keg problem.
Pretty odd given that...
So here's the kegerator I have: https://www.amazon.com/gp/product/B017HVSKRY/?tag=skimlinks_replacement-20
I've been having success with sparkling water and cider, but my first beer is giving me some problems. It worked out okay at first. Foam was a bit heavy, but that was likely a tower...
Just wanted to add an experience to this thread:
I pitched some Safale 04 into Santa Cruz Organic apple juice (and 0.5 lbs brown sugar) two days ago, and yesterday evening I noticed a sulfur smell coming out of the bubbler. It wasn't enough to fill the room with "rhino fart", and the sulfur...