It's happened to me, too. Originally, (after the SP first came out) I had the same one. He was an older Sim, an Elder, but he did a fine job. The family loved him. He was so dedicated to his work, in fact, that he went outside in the pouring rain to fix the Rock Climbing machine this very rich family had in the backyard. In fact, he gave his life in his duty. Then, and only then, was he replaced. At first I didn't understand the change in help, but it didn't take too long once the family gathered around the urn in the backyard to weep over their lost Butler. When the new Butler headed for the backyard, also during the rain, I was quick to have the various teens (four of them) find ways to keep him from his duty of fixing the now broken Rock Climber.
This was my first experience with the Butler in Sims 4. I quite liked the way the system worked. Then, I noticed that the Butlers would constantly change out. I thought to myself, either I've locked him out or failed to assign a bed to him. So, I made certain to assign the single bed for the Butler. He hadn't died, as he showed up at a concert my Rock Star was performing. But for some reason he wasn't staying at the mansion. I even had one of the teens give him his own key! This did not solve the problem. Since this latest patch, where having a maid caused the game to automatically and randomly pop into 'hyper-drive', making the game next to impossible to play, I haven't added a Butler to this family for fear it, too, would trigger this unhappy pace.
As much as I am very glad to have fixes made, sometimes, or so it seems, while some things are indeed fixed, we're all too often revisited by past bugs. :'(
