Updated by GoldenHelmet 12/27/23
The mechanics for mobs exiting rides were changed in 1.16.210. Mobs now search for blocks that can provide support around the ride that they are exiting, and will only exit onto a supporting block. This is intuitive and safe for players in many situations, especially dismounting from striders and boats that normally remain in lava or water, respectively. However, the check for support around the ride is unintuitive and frustrating when players try to use activator rails to eject themselves or other mobs from minecarts. Many systems for moving mobs to specific cells, such as villagers in trading halls, were broken by the change.

Steps to reproduce

1. Load Unintuitive Minecarts.mcworld . The test world contains 5 labelled test stations that show different aspects of activator rail ejection behavior.
2. Run each test by pressing the button on top of the command block.

Expected results

Mobs should be ejected into the space to the right of the activator rail, to the left if the right is obstructed, and on/in the rail only if both left and right are obstructed. Specifically, in the test world:

1. The villager should drop into the cell prepared for it.
2. (a) The villager should drop into the cell prepared. (b) The villager should stand on the iron bar.
3. The creeper should fall into the drop chute.
4. The creeper should fall into the drop chute especially because spaces above the track are obstructed.
5. The ravager should fall to the right of the rail line.

Observed results

Mobs in a moving minecart are not ejected ejected into the space to the right of the activator rail in most cases where they could fall into a hole/chute. Specifically, in the test world:

1. The villager stands next to the hole.
2. (a) The villager stands on the edge of the block next to the hole, failing to fall into the hole because it gets positioned relative to the minecart instead of relative to the activator rail. (b) The villager falls next to the iron bar because it gets positioned relative to the minecart instead of relative to the activator rail. (This test helps to reveal the underlying mechanic that prevents falling in other cases.)
3. The creeper stands on the rail next to the drop chute.
4. The creeper stands on the rail next to the drop chute even though that puts its head inside a solid block, and it suffocates.
5. The ravager stands on the edge of the rail line, failing to fall because the ejection offset fails to take into account its size.

When the player or a mob rides a minecart over a powered activator rail, the subject is no longer ejected to the right of the activator rail.  Instead the subject is ejected a few blocks before the activator rail. When placing glass above the rails the subject is ejected within the glass. 

I think this issue may be related to the changes regarding minecarts from the 1.16.210 update. 

https://feedback.minecraft.net/hc/en-us/articles/360057677072-Minecraft-1-16-210-Bedrock-

Minecarts now properly update their effects (looping sound, player coordinates) when the minecart is not being rendered for the rider (MCPE-104044)