The bug

The template models used for rails are not prefixed with "template", alongside having many other naming problems. (It's worth noting that I've since noticed that they're identical, giving rise to MC-237445; this bug report may be considered succeded by it.

Template models are models which have a defined shape but not textures, referenced from other models which reference those textures.

The models rail_raised_ne.json and rail_raised_sw.json respective reference template_rail_raised_ne.json and template_rail_raised_sw.json. However, the models rail.json and rail_corner.json reference models rail_flat.json and rail_curved.json.

Since these last two models are formatted as and referenced as template models, shouldn't they be renamed to "template_rail_straight.json" and "template_rail_curved.json" or something similar to signify this, possibly renaming "rail_corner" to "rail_curved" in the process for consistency?

How to fix

The resource pack attached to MC-237445 fixes this issue completely, alongside fixing multiple other issues with flat plane models.