In my experience LightDM is the biggest turd of a display manager I've ever used.. it's so finnicky, sometime when switching from X (any DM) to LightDM even though you enable it via systemctl it doesn't work. I've had the worst experiences with LightDM..
So, I'm not sure what happened with your system, but I'm using gnome3 with LUKS on ext4 and I haven't encountered any issues with recent updates. Sounds like a one-off issue to me.
I'm sorry, I have to disagree immensely. My experience with LTS and non-LTS versions of other distros with Ubuntu being the biggest offender is the prime reason I run Arch on my primary machine. Rolling release distros are, contrary to your statement, far more stable, well tested and secure, then their stagnate Debian or Ubuntu or Fedora counterparts. I've not run into a issue on arch (aside from Steam specific issues) that have cause me to think about leaving Arch.
As for LightDM, I've yet to receive any errors with it either. I must be lucky, or daft in my updating every week.
Bit of a necro, Arch patched the issue - as per usual - within mere hours. Further discussion of the fail update is not necessary. Arch users know that this happens, they're used to it, they live with it, and they don't have to live long with it, because it's Arch and patches always come super fast, and it's a bleeding egde rolling release distro like everyone knows, and the choice of distros is not the subject of the thread. So I'm locking it by lack of further relevance.