Did you try the fix above? It worked for me and hasn't reverted (so far) even after multiple computer restarts.
I was just about to give it a go when LastPass Support gave me a call and fixed the issue.
What was the fix that worked for you? It'd be good to share.
Sorry but I actually did nothing on my end except logout and log back in using my master password. The lady from Support did something on her end which fixed the problem (she mentioned killing something from her end). Sorry I couldn't add a fix to this problem.
I did try the "fix". It worked at the time, but the next day lastpass rejected my master password.
I had the same problem today with the Chrome extension. I couldn't open the protected items like credit cards etc which requires entering the master password even if the extension is logged in properly (which it was). For me the fix was simply to re-login into Chrome extension.
I tried the Fix Problem Yourself/Clear local data/Clear browsing data solution, but it didn't work for me.
To be sure I have the proper password, I tried opening Firefox and logging into the LastPass extension there including opening some protected credit card records etc, and it worked without flaws. So then I was sure I'm entering the proper password, so I did try to log out from the Chrome LastPass extension, and when I logged in again, everything worked.
Leaving LastPass as soon as possible
I'm not ready to say this works, but here is what I did.
1. I used the instructions to increase iterations to 600000.
2. As before, lastpass didn't recognized my master password. I did not revert the password as I had done in the past.
3. Instead, on the same computer, I opened another chrome profile, (my wife's). She uses my lastpass account. I made no changes on her profile. I only checked the account settings. The iterations remained at 600000 and the master password worked.
4. I returned to my chrome profile. Instead of reverting my master password, I removed the extension. I then reinstalled the extension.
4. After reinstalling the extension, I checked my account settings, and the iterations remained at 600000. So far, my master password is still working.
5. If after a day or two, if my master password continues to work, I'll validate the process as a fix.
The fix provided by pavelt999 is still working for me, so I will venture a "Accepted Solution" tag for the second time. Hopefully, this time is for real. Let me explain the steps I took to get everything working.
1. I followed instructions to increase iterations to 600,000.
2. The last part of that process is lasspass signing you out and requiring you to login again. I did that. In previous attempts, I could sign back in, but from that point forward, lasspass stopped recognizing my master password. This time I proceeded to the next step before testing my master password.
3. Immediately after "step 2", I uninstalled the lasspass extension from chrome.
4. I reinstalled the lasspass chrome extensions, and so far, everything is working.