Steps to Reproduce:

1.) Enter a nether portal while having a long pre-travel swirling animation

2.)Leave the portal when you're about to change dimensions

Observed Results:

Crashing and chunks near the portal being laggy and broken

Expected Results:

Leaving the Nether Portal

Other factors besides the Nether Portal.

1.18.3 update, large amounts of entities within the chunk, building for hour outside said chunk, spawn chunk, entering the chunks by nether

Notes:

Suddenly leaving a portal when the pre-travel swirling animation is about to end and the process of changing dimension from overworld to nether is about to begin, causes the game to crash. When you join back in the world, the chunks around the portal are broken and cause huge lag spikes.

When joined by another player that is located in a different area, the player doesn't experience the lag spikes and has normal gameplay; however, when the player goes to the broken chunks, it causes the game to also crash. The world is a single player world created on the Aquatic Update.

It occurs if the dimension change with the nether portal isn't instant. 

The mobs move in the affected area, sometimes you can open chests or your inventory, the chunks near the affected are won't work. 

Older copies/backups of the world work fine however it is not certain if corruption will also happen within a few more hours of gameplay.

It is possible to escape the corrupted chunks by somehow managing to get in the nether portal and escaping by nether.