Lastpass will sometimes tell me to turn on accessibility to my device. Accessibility is already on in system settings but the system says that the service is malfunctioning. I am sometimes able to use autofill and sometimes it will not work.
Apologies as I'm not sure what steps you've tried so far. Could you try first uninstalling the LastPass app, restarting your device, then reinstalling the app and trying again? You may need to re-enable autofill as well: https://support.logmeininc.com/lastpass/help/how-do-i-enable-and-use-autofill-in-the-lastpass-passwo...
If that doesn't work, could you try only enabling Legacy Autofill to see if that fixes this issue? Steps to enable legacy autofill are outlined here: https://support.logmeininc.com/lastpass/help/how-do-i-manage-my-settings-in-the-lastpass-password-ma... (under the "Autofill in Settings" section)