how do I fix this?

Im trying to give some towers in my map %chance to cast an ability, so I think lighting orb of course, however it wont work really its bugged kinda

I give it 100%chance to cast (just to test) and it never works at all when units come in range....... however it works fine if I click A(attack) then attack the unit. Has it always been that way? How can I fix it it

I tried it on a hero just to see if it was a tower bug, and sure enough my hero wont ever get the proc off either, unless I click the unit, or attack move also works and any units I hit the spell will go off, but if I then click move to somewhere the ability will no longer work once again, untill I click attack

It's a bug. To make it work, you should either wait for it to be fixed by Blizzard in a patch, or trigger it, like Lord Vexorian does with his stackable orbs.