Iron golems shouldn't spawn on top of lightning rods, but they do that in my iron farm (picture attached). This was observed on the Xbox Series X in version 1.17.41. I haven't tested on other platforms yet.

This issue is related to MCPE-140145. Based on the discussion in that bug report I believe it is not intended that iron golems could spawn on lightning rods because they're not full solid blocks. 

Steps to reproduce:

1. Make a working iron farm and place a few lightning rods above the spawn platform (not too high above the beds).

Expected result:

Iron golems will never spawn on the lightning rods

Observed result:

Iron golems can spawn on top of the lightning rods and will stay there indefinitely, which stops the iron farm from working.

Note: It may take a while to see this bug depending on the ratio of lightning rods to other spawnable spaces.

Note 2: I have only tested lightning rods in the upright orientation as shown in the picture