Actually, the "sneaking" status is seperated into two parts in 1.14. The first one is bounding box sneaking, which lower the player's bounding box height to 1.5 and eye height to 1.35, and does not have any other effect. Another one is control sneaking, this prevents the player from interacting with blocks or falling off edges.

Bounding box sneaking happens both when the player is holding shift (while not flying), or when the player is sneaking pssively in a 1.5m high space. On the other hand, control sneaking happens when the player is holding shift, no matter it is walking or flying or sneaking or crawling.

This mod forces control sneaking to happen even when the player is sneaking passively, and prevents control sneaking while crawling. This does not match the 1.14 behavior.

Btw, I do not know how to fix it because sneaking isn't seperated in 1.12. Maybe requires major changes to the mod.