Sometimes, very occasionally, when using the Lastpass plugin with Google Chrome, you may find that Lastpass will start acting wonky. Specifically, if you've had Chrome running for a couple of days, you will notice that Lastpass has logged you out, even if you're in an Incognito Window. When clicking on the browser plugin's icon, you will be able to log into it as usual; multifactor authentication will similiarly work as expected. If you wait a few seconds, the plugin's icon will go dark again. If you're quick and drop into "My Vault," you'll see that screen for a second or two before you get bounced out again. You won't be able to log into anything, and you'll eventually start cursing the day you decided to stop using a password manager like Keepass. You might do this a dozen or two times, scratching your head all the while.
To break out of this frustrating loop, clear your browser cache (Chrome menu icon -> History -> History -> Clear Browsing Data, check Browsing history and Download history, uncheck everything else -> Clear browsing data), fully terminate Chrome (don't just close all of your windows), and start it up again. That should fix the problem.