Arrows can be shot at and not go through a portal under special conditions

Issue: A large percentage of arrows shot by a skeleton or even the player into a portal in the Nether that connects to several portals in the Overworld, skip the portal and stays in the Nether, continuing on its normal arc as if the portal wasn’t there. It doesn’t happen if there is only one connecting portal in the Overworld. The first version to show this arrow behavior is 24w33a, the first snapshot for 1.21.2. It does not occur before this version, but exists in all versions from 24w33a to the time of testing, 1.21.5-RC1.

This issue may be related to another issue I reported, MC 295670, but requires several different/additional conditions, like the extra portals, to reproduce so I realized it needed its own report.

Setup: This occurred in a world where I built Nico Is Lost’s portal based iron farm. In the Overworld, it has three levels of oversized portals with seven per level with a two block space between for a total of 21 large portals close together. They all connect to a single regular sized portal in the Nether. In the Nether, I placed a boat with a skeleton on one side of the Portal, and an Iron Golem on the other side so the skeleton would try to shoot the golem and the arrows would go through the portal and keep the Overworld loaded, otherwise my Iron Farm would shut down when I came to the Nether.

Findings: Some arrows would go through the portal as desired, but many would not and pass through the portal as if not there and hit my golem or stick into blocks near him. I created the same setup in a test world, but with only one portal on the Overworld side. I could not reproduce the problem until I added all the extra portals in the Overworld that was part of Nico Is Lost’s Iron Farm. I could then even shoot arrows myself and get the same behavior. It seems to happen more when shooting at a bit of a downwards angle. My skeleton is 3 blocks higher than the golem he is aiming at, and 8 blocks between them. The portal is one block closer to the golem. After seeing the problem, downgrading the world to any version prior to 24w33a, and the behavior will not occur. Re-upgrade to any version 24w33a or later up to 1.21.5-rc1, and the behavior will return.