I contacted support and was eventually able to get Lastpass to Autofill Edge on Android.
I tried their first suggestion but it didn't work:
Please check if autofill is enabled on your Edge on Android, if it is enabled, then uninstall Edge, power cycle your device, install Edge again and test the issue.
The second instruction was successful though.
1. Open LastPass app > Settings > Actions > Clear LastPass Cache
2. Open LastPass app > Settings > Actions > Refresh Vault
3. Logout, log back in and test the issue again.
Hope that helps anyone else having problems.