It appears to be a flaw in the OS, mostly experienced on older Intel Macs but others have reported it. The symptoms seem to be:
- Sometimes works as expected, touch ID is offered immediately as an option when waking the laptop.
- Sometimes, initially offers only password entry as option, but after waiting for 5-10 seconds (some have indicated a bit longer than that), then both password and touch ID are offered as options to get past lock screen. During that short delay, the user images flash off and on a few times, finally stabilizing with touch ID offered to use.
I see this on an Intel MacBook Pro 16" 2019.
It seems moralize a mild inconvenience than anything else because no real harm derives from it.
If you can't use touch ID at all, that's a different issue.