I don't know, I can't find anything that justifies that difference in performance, but both times I had to format my phone while using an eSIM, I lost it. I had to go to one of my carrier's stores to get another one, but nowadays that's a hassle because I don't have one nearby. That's why I'm afraid of restoring and losing it.
What do you mean by “format”. Would help if you outlined the steps you take. They should basically be:
1. Open iTunes
2. Plugin your phone to the pc and wait for it to show in iTunes.
MAKE AN ENCRIPTED BACKUP !!!
3. Press volume up, volume down then press and hold side button until you see the connected to pc message.
4. Then follow the prompts to restore.
The pc will download the correct file. When that’s complete just follow the prompts.