On July 2, Second Life users using the release version of Singularity Viewer started experiencing bake fails (avatar as cloud), inventory issues and other problems. Turns out Linden Lab formally turned off access to some server-side APIs grid-wide that had long been scheduled to be shut down. Apparently Singularity had some leftover code tstill using those APIs causing the issues.
At first the Singularity devs recommended switching to one of the nightly development builds but that turned out to create new problems (those things are generally alpha releases and not suitable for primetime). A couple of emergency roll-outs later and things are more or less back on track. Assuming you want to mess with nightly releases, here's the link: https://virtual-nexus.xyz/down/
For a more complete (and technical) write-up about what happened, read Singularity Goes Sideways from Nalates Urriah's blog. (If you aren't subscribed to her blog you should be!)
Now if you're like me and don't really enjoy messing with alpha releases there is an alternative -- Cool VL Viewer. It's lightweight and easy on lower powered systems, uses the classic interface and is actively maintained and updated reliably. For more details and downloads, visit: http://sldev.free.fr. When I need better framerates and want to run more than one avatar at a time, I use Cool VL Viewer. It's been very solid for me.
Yes I can hear you yelling "BUT SNICKERS! IT'S NOT ON THE THIRD PARTY VIEWER LIST!" No it's not. The developer, Henri Beauchamp, states that it is TPV compliant but he doesn't want to release his private info to Linden Lab AND he believes the laws in France say that he shouldn't have to. That's fair and to his credit, I have never heard another developer EVER question whether Cool VL Viewer was safe or not.
I really do hope Singularity can get back to having a solid release version since the more lightweight, capable viewers there are, the better.
UPDATE: If you do want to continue using Singularity, UNINSTALL your current version completely and (as of this writing) install version 7685 from the link above!
NOTE: Users are reporting issues with the Android Lumiya Viewer that sound somewhat similar to the Singularity problems. Since Lumiya hasn't been updated for over a year, it wouldn't surprise me if the two were related.