Comparators will not update to reflect the amount of signal strength from a hopper, dropper, or dispenser block in the latest snapshot.

Steps to recreate.
-Create a new Minecraft world using the 17w47b snapshot
-Place a hopper/dropper/dispenser with a comparator facing out of it
-Place items in the hopper/dropper/dispenser
-Observe that the comparator will not turn on

Updating the comparator will force it to work, but will only work if it is constantly updated. Will still output signal after items are removed.