Is this an normal Wc3 bridge or imported one?
Are the patching blockers set down to the bridge or not?
...
1st picture :
Maybe this has something to do with unwalkable too...
Did you set that bridge on walkable or not...
If not then go to object editor,go to destructibles,and then go to bridge/ramps,then chose whatever you want there...
2nd picture :
You set the patching blockers under the bridge so now you done 2 things...
You set that side unwalkable and with patching blockers that are set under the bridge you actually caused that bridge to be blocked to.