Ok, yeah I researched it a bit and looks like it doesn't clear any setting or anything.
I got a system update over the weekend and before I try to clear the cache I want to see if Samsung fixed the issue in that update. If not, I'll try clearing the cache.
Clearing the cache partition on Note9 seems to have worked for me.
As of this morning, it was not working, and no new updates to apply.
I entered the boot menu by holding the Bixby and volume up buttons while powering up after a full shutdown and then cleared the cache.
If the issue returns, I'll update this post.
@charlesrbasin Have you tried removing the trusted device then re-adding it?
Yes, removing the trusted device and adding it back did not make any difference. I also have a Sumsung Galaxy Tab A tablet running Android version 9, and Smart Lock works reliably all day long. The phone also worked without any problem before the update from Android 9 to 10.