Could you try to save the entry in your Vault using the Save All Entered Data method as described below?
Make sure you are logged in to your LastPass browser extension.
Go to the website whose login you need to force-save.
On the login page, fill in your credentials (username, email address, password, etc) but do not press login.
Click the LastPass browser icon, then go to Add item > Save All Entered Data at the bottom of the menu. Tip: For Internet Explorer users, click the active LastPass icon, then go to Tools > Save All Entered Data.
All captured fields are displayed. If desired, enter more information and specify your desired settings for the item.
Click Save when finished
Once saved, when you return to the login page LastPass should fill the data for you. You can also “force-fill” the login from the LastPass notification bar, or from the LastPass icon by selecting the site name at the bottom of the menu and then clicking “autofill”.