You could try saving the hospital lot to the library then bulldoze the current one and replace it. If that doesn't work, you could build the hospital elsewhere (when you are building on a community lot, there's a special community buildings icon in the build menu, all the community buildings are there, just not on lots, so you can build your own lot). You also could have an invisible car causing a problem. I use the NRaas Overwatch mod for this type of clean up. Routing can also be bad. Every world EA has put out has some sort of routing issue whether it's roads not properly connected and such. I've resisted getting the 'fixes' for them because you have to re-apply them after every patch. But to me it sounds like someone on the lot or something on the street is borked. Overwatch is a 'clean up' mod. It will sort out stuck sims, excess cars, that kind of thing which can lag your game. I remember I once had a Margaret Vaguester car stuck outside a house on the street that I couldn't get rid of until I got Overwatch which cleaned it up for me. Silly cars.
