This bug is a parity issue. When you try to fill the cauldron using water/lava drips from the dripstone, it doesn't fill the cauldron at all.
How to Reproduce
1. Create a water/lava source.
2. Place pointed dripstones (at least 3-4 blocks tall from top to bottom) underneath the block below the water/lava source.
3. Place a cauldron below the dripstone.
4. Either wait or speed up the random tick speed.
The cauldron doesn't get filled up.
The cauldron should be filled up with Water/Lava.