Ok so this is a bit of an odd one. I'm a superuser on the NOW TV community and a web developer by trade.
I reply to most messages on my Nexus 6 running Chrome Beta mobile in desktop mode.
This has been fine until beta reached 48 when suddenly the @mentions stopped appearing. At first I had thought a new/changed api in Chrome 48 was the issue, however it's fine on my Win64 version. I've tried running debugger to see if any errors are thrown in the console but I've not found anything.
If I use Chrome mobile 47 I'm fine.
I've tried switching my desktop user agent to
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.71 Safari/537.36
but that works fine to.
I get the same issue if I try to reply on these forums suggesting the issue isn't NOW TVs, although if it's Lithium, Chrome or TineMCE I don't know.
Any of the Lithium devs got a clue to what's going on?
Sounds like an issue with Chrome beta since the other two variables (Lithium and TinyMCE) haven't changed.
I used to run alpha and beta builds of Chrome and Firefox and ran into issues similar to what you're describing from time-to-time. They were almost always resolved by the time the GA release arrived.
Life in beta - not for the faint-of-heart.
This issue has cleared up today. Not sure if it's Chrome Beta 51 which has done it, or a backend change to Lithium or TinyMCE.