Put the summary of the bug you're having here

What I expected to happen was...:
A new portal would generate at the correct coordinates

What actually happened was...:
No portal generated and I fell through the air into lava before I could do anything

Steps to Reproduce:
1. Enter the Nether through a portal in 1.15.2 and then go back through it
2. Update to 1.16.1

3. Reset the Nether
4. Go back through the portal