Minecraft, catching fire when coming through nether portal

The problem was with the overworld portal.

After wasted a few hours more trying to rebuild the portal on the nether side, I decided to rebuild the portal in the overworld "few blocks away", didn't count how many because didn't expect it to work, but it did.

Then I placed the portal back to where it was and the problem came back as expected.

So I

• Step by step removed all adjacent blocks from the portal and tried entering after every removed type - didn't work
• Cleared more then just adjacent block - didn't work
• Rebuilt the portal one block upwards didn't work
• Rebuilt the portal one block inwards - had high hopes on this one because "few blocks away" worked - but didn't work
• Rebuilt 2 blocks inwards - worked, but - only once, after the next try I caught on fire. Thought it was because I activated on the left bottom step and entered from the right but after numerous attempts didn't manage to get it working again

Disappointed that 2-blocks didn't work, I built it on the other side of my little room 9 blocks away and it worked! Sorry I couldn't bother to try what was the minimum amount of blocks from 2-9, but I guess because the problem didn't appear on one certain block, the minimum amount wouldn't be accurate anyways.