Please watch the video here, starting at the timestamp (10:51) to about 11:55.
https://youtu.be/vkuMDLOhCv8?si=-zjTIGWowx0KqxaS&t=651
Comparators seem to be reading the contents of chests in a directional manner. This is therefore resolved by orienting chests in a certain manner, so this is very unintuitive.
Adding to my above comment, while this may not be a strict bug (since double chests are actually two single chests with a fused UI), since double chests act as one from the player perspective, this should be patched to make the user experience seamless.