In a small cell, made out of 18 wooden chests (9 double-chests, actually), 1 copper chest, 3 slabs and 1 stair, the copper golem can’t see the wooden chests on the second row, first and third column (or the right and left chests of the second row, as you prefer), if they’re aligned on the east-west direction.
All chests contain the same random item (in this experiment, it’s a stone brick slab), and the copper golem is given a stone brick stair. This experiment was made to check if the copper golem would have any problem detecting any of the chests, which it did. That’s why I didn’t give him a slab, because he’d put it on the first chest that he opened and wouldn't try to open the others.
This bug doesn’t happen if the cell is aligned on the north-south direction. And can also be fixed with small changes on the design of the cell (removing the slabs on the sides and adding more stairs to the bottom, and some walls around the golem, so it doesn’t escape), but it will make the process of sorting items take a little longer.
It’s a little bit curious why it does only happen if the chests are aligned on the east-west direction.
I noticed this bug happening both on Android 15 and Windows 11, latest version of Minecraft Bedrock (1.21.114).
Below, you can see some screenshots that show the composition of the cell; the cell with chests and the golem, and a third screenshot with signs that explain a bit about the problem. It is important to say that the screenshot of the cell that shows the golem is different than the other with signs.
Both of them have the same things (including the golem), but the one with signs is aligned on the east-west direction, while the other is north-south (in this one, the copper golem can detect all 9 double-chests).
To reproduce the steps, you can create a new world on creative mode, make two cells (materials listed on the post above and on the screenshots) in both east-west and north-south directions.
Put the same one item in every double-chest of both cells, give a different item to the copper golems (they’ll never find a chest to put the item in), and check if both golems can detect and open the right and left chests of the second row. It’s important to make the cells 64+ blocks apart, so the golems can’t detect the chests from the other cell.