Hello,
Apologies as I'm not sure what steps you've tried so far, could you try uninstalling the LastPass app, restarting your device, then reinstalling the app and making sure autofill is enabled per these steps: https://support.logmeininc.com/lastpass/help/how-do-i-enable-and-use-autofill-in-the-lastpass-passwo... to see if it fixes this issue?
If you've tried uninstalling and reinstalling then making sure Autofill is enabled, this may be a bug. So that our team can gather more specific details and hopefully fix this, could you submit a bug report following the steps here? https://support.logmeininc.com/lastpass/help/how-do-i-report-a-bug-to-lastpass