I have been able to do a renovation in an apartment. A sim family with a child were living in a 1 bedroom. I was able to add a 2nd bedroom by dividing the 1 bedroom to create a larger and smaller bedroom. I was able to delete items and renovate without a problem. So this may be something that your game is experiencing but others aren't. I once had a gig in which I completed it but didn't get paid for it. I thought it was a bug, but the next gig went as it should have. As frustrating as the situation sounds to be, maybe trying another apartment gig will not yield the same results. I'm just another player trying to help brainstorm for this situation. If it doesn't work on a different gig, I hope it resolves soon for you.
I went to an apartment in Evergreen Harbour and the game did not allow me inside, the whole level was in grey color and there was no option for knocking the door either. I only talked to clients in front of the door (lol) and got their preferences just in case, in build mode thank God i can finally see inside the apartment. After the renovation and going back to live mode, the house got completely grey and unreachable again; I clicked on my sim and called clients back, then finally, there was the option “knock on door” with the interior designer symbol beside. Well, it was supposed to be there at the very beginning. The rest of the process was without issues.
