This happens on Android 8.0.0 with all versions of the Android LastPass and PayPal apps. I keep them up-to-date.
When I launch PayPal, the app asks for my password. LastPass presents the autofill dropdown. I select that. The password appears for a second, then disappears.
With biometrics on, the PayPal app asks for my fingerprint. I scan my finger. It jumps to the password screen, where the above happens. I am then returned to the PayPal biometrics screen.
So in general, the only way to get into the PayPal app is to ignore the autofill prompt, and copy the password from LastPass.
Can this be fixed, or can a feature be added to exclude some apps from autofill?