I asked around with some friends, and got a mod suggestion - since you are willing to use mods, look up Zerbu's Venue Changes mod and try that on your test copy to see if it lets you switch the lot type back to medical clinic.
It seems as it is just this one, I have tested a couple of other saves and the issue is not in them.
I’d suggested doing a “save as” to get a copy of your current save we can experiment with then. Do you have mods?
In the copy of the save, check that the problem still exists, then remove mods and test again.
I did as you wrote (and thank you btw) but the result was still the same. The only mods I have in my game is MC comandcenter, and I tried to save as with and without mods but with no luck.
I asked around with some friends, and got a mod suggestion - since you are willing to use mods, look up Zerbu's Venue Changes mod and try that on your test copy to see if it lets you switch the lot type back to medical clinic.
