The Copper Golem is unable to open bottom chests in the following scenarios:
When a bottom chest is surrounded by blocks with another chest placed above.
When a bottom chest is surrounded by slabs with another chest placed above.
When a double bottom chest is surrounded by slabs, leaving one air block, with another chest placed above.
Depending on the Copper Golem’s facing direction, this angle may change.
Example: if the air block is on the left and the chest is on the right, the Golem cannot open it.
But if both the air block and the chest are on the same side ( both on the right), the Golem can open all three chests (bottom, middle, and top).
There is also a rare case where the Copper Golem manages to open a bottom chest surrounded by slabs with a chest on top. However, when this happens, it gets stuck in a loop trying to open the top chest.
Seems related to MC-301979