The password is likely saved to your browser's password manager, and it's overwriting the field. Please check that list, and delete any LastPass items. Also, if it says https in the URL bar, then you are in the web interface. Consider using the browser extension in the toolbar instead.
Installation instructions: https://support.lastpass.com/s/document-item?language=en_US&bundleId=lastpass&topicId=LastPass/install-lastpass-extension.html
FAQ on how to check and remove browser password manager data.
Chrome: https://support.google.com/chrome/answer/95606?hl=en&co=GENIE.Platform=Desktop#zippy=,check-your-saved-passwords
Edge: https://support.microsoft.com/en-us/microsoft-edge/save-or-forget-passwords-in-microsoft-edge-b4beecb0-f2a8-1ca0-f26f-9ec247a3f336
Firefox: https://support.mozilla.org/en-US/kb/edit-or-delete-login-firefox-password-manager
Safari: https://support.apple.com/en-us/105115
I am having the same problem but I cannot find an answer!
Thank you jpenny84 - the same issue cropped up for me unexpectedly and your answer helped resolve the issue!
That worked!! Thank you so much for sharing that fix!!