If you have a model that has translucent parts in it, you will be able to see pretty much everything through it, except for the other parts of the very same model which are behind it
Example:
Expected appearance

The appearance with sodium

P.S. The redstone block is rendered separately, it's not a part of the model

Ig the item in hand is untouched by the sodium renderer so that's why it is not broken

Possibly duplicate of #38

I think this is somewhat different, the parts that are not rendered are part of the very same model, but I guess could be related

Also a simple test to see if it is related to #38 is if the model looks correct when viewed from 1 or 2 sides(north, south, east, west), but wrong from the opposite side(s).

What model is the model in your example from? I can try and reproduce the issue.

Made it in blockbench, blockbench has the same issue rendering translucent objects

Caused by #38. See that issue for more information.