Update to server caused Nether deletion

Today, the server host updated to MC 1.11.2 from 1.10 and they realized that the entire Nether was erased, and in 1.10 there were multiple portals there, but they were erased. Everything disappeared, but the Overworld was fine. I apologize for the server host not reporting, but they are trying to fix what was erased. The nether was already generated BEFORE updating to 1.11.2 but AFTER the update, I went through a nether portal and the Nether began to generate, as if it hadn't existed.