I've been using 1Password on Mac, Windows, and iPhone for more than a year now. Version 18.104.22.1684 works fine for me on Windows. I'm not doing anything fancy with it; no Team or Family. I store my vault on Dropbox. My password does not contain any non-ASCII characters.
Tonight I installed the 1Password for Windows 10 beta from the Windows Store and tried it (and I made sure I did not have 1Password 4 running at the same time). The beta version has me log in to Dropbox, select my vault (it's the only one shown), then it asks me for my 1Password vault password, but it doesn't accept my password and it won't unlock my vault.
I can quit it, launch 1Password 4, enter my vault password there, and get into my vault without any problems.
1Password Version: beta
Extension Version: Not Provided
OS Version: Windows 10
Sync Type: Not Provided