Adverse possession is extremely misunderstood. It almost never applies to landlord/tenant type situations.

The reason being that that posession is not “adverse” in the sense that the person was living there with permission in exchange for rent.

Adverse possession, generally, comes into play with property line disputes, and sometimes with genuine long term squatter situations.

A core and often overlooked element however is that a license or permission to use the property means you aren’t possessing it “adversely”.

Adverse possession wouldn't wipe out a properly recorded lein. Of course, it doesn't seem that the lein was properly recorded. You could maybe sue the leinholder to provide proper documentation or abandon the lein, but you run the risk of the leinholder finding enough documentation to convince a judge, and making the lein valid and enforceable, instead of vaguely maybe not an issue.

Or, maybe you just pay someone to "find" the documents, and hope the leinholder doesn't notice or doesn't care. This case seems murky enough that even a potential recovery of $1M might not be worth it for the leinholder.

Some states allow a civil suit against all known creditors, lien-holders, or anyone else that may have an interest in the property, forcing them to show proof of their interest, then the judge makes a declarative judgment stating who owns the property, and the obligations the owner may have to the other parties.

Statutes enabling such suits are custom-tailored for removing clouds. If the lenders don't have their paperwork in order, the judge can sever the mortgage from the note, turning it into an unsecured debt.

For anyone curious this is typically called an action to "quiet title"