Animals dropping through bridges, mobs coming up from under them

[Audrel 2,223]

I unhitched the bulls from my wagon in their field that is attached to the 2nd floor of my house with a 2 tile bridge. They immediately used the bridge as a door to escape the pen and run amok. While I was headed to the house to go down and out because they were on the lower level tier at this point and that is the fastest route to catch escaping animals, a spider came up through the bridge to attack me. 

 

I had to remove the gate from the end of the bridge because it wouldn't open most of the time and kept me locked out of the field. Now what I removed it, this happens. 

[Zachariah 736]

I was bringing a champ Lava Spider across a bridge that goes across water and it was on top of the bridge but it stopped moving halfway across and started to drown.