For some reason on my world, when I wire up my heart and mana statues, only one of them works. If I remember correctly, they both used to work but for about the last month or so one will work and one won't. Any ideas why this is happening or how to fix it?
There have been changes to the wiring system which may be causing the differences you are seeing. Relevant parts I have emphasized.
All statues (even those that appear shorter) have a footprint of 6 tiles (2 wide, 3 tall). Each of these 6 tiles could be used as a wire input. Since 1.3 update, each input shares cool down period with each other after activation. During an input's cooldown, activations from any trigger devices (switches, timers, pressure plates) will be ignored. For enemy & critter statues, this cooldown lasts exactly 0.5 seconds. Item statue inputs have a far longer 10 second cooldown.
Also note the table in the link that states item statues (hearts and stars) can only have 6 items spawned per 50 tiles in any direction.
It's possible that there was an update which makes the statue don't work, or it's a simple bug. Try replacing it but I think you already did that.