22 hours ago, Fibbonacci said:They would stop on the bridge and attack the block connected to the support. this seems like very odd behavior, and I would like to understand why the zombies are doing this to help my base design in the future.
As mentioned, there is a state called "destroy area" which is triggered when a zombie's path is broken or interrupted and take damage. This is most apparent if you are on an elevated fighting position. If they get knocked off, they will likely take fall damage and go into destroy area which will last for a short period of time (I think it's something like 15 seconds) after which they will attempt to path to you again.
That being said, what you are describing here is somewhat new in A21 and I do not know yet what causes it. I've observed it myself and it's slightly annoying. In past alphas, the zombies would never stop in the middle of an elevated path and start beating on it unless they couldn't get to you. For now, I would just make sure that the main path is strong (concrete if you can) and is regularly repaired between blood moons.
It's possible that a new mechanic in A21 is partly to blame. See, zombies will not go into destroy area if, after falling, they are more than 11 blocks away from the player. The reason for this is fairly simple: it reduces the load of the AI and makes for better performance. This means if you make your base tall enough, there shouldn't be any real danger to the supports below your fighting position (unless a cop or demo explode next to them). The thing is that if they get within the 11 blocks too quickly, their destroy area mode will still trigger. It's entirely possible that this is playing into the weird behavior of them stopping in the middle of the elevated path and beating on it. Ensuring that their path back to you is a longer one might help with the issue, but I haven't done enough testing on that yet to say for sure.