Google Nexus 5 :: Why Won't Phone Boot Past Colored Symbols

I have had my fantastic Nexus 5 for some time now, and up until the Android 6 update I have had no crash issues at all. It may be coincidence, but since the update a couple days ago my phone has crashed three times, and with the last crash it will not boot past the colored symbols. In fact it will cycle the symbols without end at times, but sometimes it will cycle them for 30 seconds or so and then crash back to the black screen then to "Google" followed by the colored symbol screen. Rinse and repeat.

I have tried full shut off and re-start by holding down the power button and that does nothing new. I read on these forums a suggestion for a Nexus 4 user back in July to try holding down the power button and tapping the up volume once to pull up some options, but that seems to do nothing. Perhaps I am doing it at the wrong time though.

I read that Marshmallow handles permissions differently, so I wonder if it has to do with my third-party launcher. Though it seems strange that I was able to (until today) use my phone just fine between crashes for several days after the update.