Smart Lock will ask for your PIN if you've been inactive for a period of time. Is that what you're seeing?
I find with my Samsung S20 that a more reliable method of keeping my phone unlocked at home is to use a Bixby routine to detect when I am connected to my home wi-fi. Don't know if Pixel phones have a similar capability. The in built Smart Lock device and location detection is very hit and miss by comparison.
Mine only does this if lock it with the power button and I have lock selected from settings...does it do this is the screen times out on its own? As mine stays unlocked.
Try unchecking that box as the description says it shouldn't lock in a trusted place but I do not think it is working. So yes mine locks up in a trusted place also when I lock with my power button. Setting/Security/Screen Lock/Power Button Instantly Locks
Think I might have cracked the code. Settings - Apps - Maps - Battery - Select Unrestricted.
Then open Maps app and press GPS/location icon along lower right side. Your location should update. Especially if you see the GPS/location icon appear in your notification panel for a few seconds.
I think the fingerprint sensor may still appear, but just swipe up. I switched back to optimized after doing this, but people might need to leave it in unrestricted.
It will only stay unlocked for 4 hours.
I turned selected unrestricted then switched the app back to optimized. I haven't had any issues. I suggest trying that to see if it's necessary to keep the app in unrestricted.
The 4 hour unlock is part of Smart Lock feature by the way.