I would let the tenant know that you are the landlord and not law enforcement.

Also check involuntary lien searches such as code enforcement, utilities, etc. 

As far as whether you're doing anything illegal by living there, it's doubtful you would face any personal legal implications by residing in the apartment (I'm not a lawyer, so I can't think of all the possibilities here), saying that, the landlord could face legal consequences and you could be forced to move without much or possibly any notice if for some reason the local code enforcers decided to come down on the landlord for the apartment being there.There are reasons for these codes and it mostly comes down to safety, so that is something to think about.I once bought a property that had a whole extra house the city didn't know about and the city did ask me to not use it as a residence (luckily that's not what we wanted the property for and it wasn't a big deal for us)

The same is true of judges, who will make or break your case when it comes time to enforce your leases.3) You can more easily develop and maintain face-to-face relationships with contractors, investors, agents and city leadership in your area.4) Even if you hire a manager, you will have to inspect how your manager is performing in person at lease 3-4 times per year until you have several years experience with that person/company. 

Generally speaking, the liens will remain if they are federal or state liens, some code enforcement liens, and few others.   

These are placed by the municipal code enforcement office and at least for my county even though nuisance lien info is available online to view, rolling fines are not.

Not having a complete chain of ownership from lender to current Seller creates issues with the enforcement of note and security agreement.Generally speaking purchase and sale contracts prevent any type of arm's length assignment of contract.

Quote from @Michael Dallas: If you have rules, you have to be prepared to enforce them. 

You would need to do your due diligence and research each property very deeply as some local lien won't be revealed without a deep dive with local code enforcement.

If not, maybe try contacting local law enforcement?