Loans and mortgages were sold by the banks to other companies:

https://en.wikipedia.org/wiki/Mortgage-backed_security

A lot of mortgages changed hands several times, the original bank who setup the mortgage would have no longer been involved at that point.

That doesn't explain how OP was able to get the lien on the land title removed when they sold the house.

It's weird to me. You need to know who to pay the mortgage to. The bank would have to notify you immediately when and whom they sell the mortgage to if they ever sell.

Unless they don't notify you on purpose to continue to receive the monthly payment, while cashing out on the resale, in which case that's fraud.

I can also imagine that the next buyer would try to pull the same trick. That obviously causes a problem. It seems to be what happened in the US, in which case everyone should check their mortgage to make sure who owns it.

You don't make payments to the lender. You make payments to a payment servicer hired by the lender.

Until midway through the Obama administration, nobody had any obligation to notify you if your mortgage was bought or sold. Payment servicers had no obligation to tell you who they were forwarding your checks to. Your mortgage could be bought and sold multiple times, but as long as the same servicer was used, you'd never know (there were/are only a few big servicers). If the mortgage buyer used a different servicer, you'd get a letter from your current servicer about the new servicer you should send your checks to, but no info about who now owned your mortgage.

I see how that could mean that the borrower might not know who owns the loan, but surely the payment servicer knows? Would they simply not tell you, even if you asked?

Exactly.

The servicers existed to serve as a smoke screen for mortgage securitization shenanigans. The servicers sent the payments to trusts that had dubious possession of the mortgages.

Trusts and banks passed ownership of mortgages amongst themselves, though tax law was supposed to prevent them from doing so. Ultimately the servicers had no more idea of who actually owned the mortgages than the homeowners.

Thank you very much for the explanation.

A judge can apply corrections in the local land registry. They're obviously conservative in doing so, but bad entries can and do appear, and judges, when presented with the right evidence, can repair them.

If there are court proceedings attached to the sale of the house, the corrections might be done there.

the loan was presumably sold off, and then again, and again, and again... and suddenly there was divergence, and it was sold off yet some more