The bug

In very early 2019, cauldrons were changed such that the interior faces would be culled if a block existed right on top of said cauldron, since there was no way of actually being able to see these faces outside of Spectator mode. A later 1.14 snapshot, however, implemented crawling, which allowed for the insides of cauldrons to be inhabited in Survival gameplay while a block was on top of it. The face culling results in the effects of MC-206620.

How to reproduce

1. Build the contraption shown in the screenshots below
2. Using the trapdoor to initiate crawling, enter the cauldron, then pull the lever
3. Note that you can see clearly outside of the cauldron while in it (MC-206620)

Expected behaviour

The interior faces of the cauldron would not be culled, since it's a region the player can enter in Survival without exploiting glitches

Actual behaviour

The model file, assuming the player cannot enter cauldrons like this, still has interior faces set to be culled.

How to fix

This is another simple model fix, as all that needs done is the removal of cullface from these five specific faces (where the cullface is "up", but the face plane direction itself is not "up", excluding for the bottom interior, which can then be seen to not be flush with the top face due to its low y "to" value). The resource pack attached fixes this issue in its entirety, and can therefore easily just be copied into the jar file to fix this (as usual I give full permission/rights to Mojang to use this).

The resource pack also completely fixes MC-205095, removes the line that disables ambient occlusion as it wasn't doing much anyway besides making cauldrons visually inconsistent from other blocks, and also tidies up the model code to make it easier to read.