Got called out for using modified version so i launched clear 1.21 update on brand new single player world
If comparator is detecting from a chest placing full block over chest then comparator makes it not detect a chest until blocks are removed and chest opened, if there is a solid block at anypoint on opposite side of chest 1 block higher it will make comparator fail to detect chest opening as a update resulting in need of replacing comparator or making diffrent block update next to it to fix it.