When ever I lead-up a minecraft Iron golem (put an Iron golem on a lead) after I remove the lead I find that its path finding is abysmal, specifically when attacking mobs. To test this simply make an Iron Golem, use a lead on them and take them a significant distance away from the starting location by dragging them with the lead, take the lead off, and spawn a skeleton a few blocks out of their hit range. Skeletons demonstrate the issue the best because they don't rush the iron golem and instead pepper it with arrows. In all of my experiments the Iron golems sees like it wants to attack the skeleton but can't find out how to get there. There are other people with similar problems like:

https://bugs.mojang.com/browse/MC-151439

and

https://bugs.mojang.com/browse/MC-153329

which may indicate where in the code the issue lies. However this issue is different than the links and does warrant its own ticket. But again I think the issues are linked some how.