Question: According to RAW, should forcing stuck/locked/barred doors open be a Strength check, or a Strength (Athletics) check?

As I read the description of the Strength ability and the Athletics skill in the rules, it seems that brute force checks, such as pushing/shoving/kicking or pulling open a stuck, heavy or locked door should be a simple Strength check, with the Athletics skill applying only to things that involve more coordination such as jumping, climbing, or swimming.

However, in the published Dungeons & Dragons adventures, examples are inconsistent. Other than the Starter Set, where all door checks are just Strength and all Athletics checks involve climbing or other more complicated activity, other supplements seem to contain a mix of Strength or Strength (Athletics) to force open doors, seemingly at random within the same adventure.

For example, in Curse of Strahd area K74, opening the 5-foot-submerged iron gate to a row of cells requires a DC 10 Strength (Athletics) check, but opening the 5-foot submerged locked/barred gate to any particular cell is a DC 25 Strength check. The only difference is the latter is locked. But then in K78 opening the locked door is a DC 25 Strength (Athletics) check, so being locked/barred isn't the determinant.

What do the rules specify should be the standard check to force open a door, gate, portcullis, etc.? When do they say Athletics skill should apply, if ever? I'm not asking about DM preference (because I realize any DM can vary any rule any time they feel the need), but what the RAW and RAI state, and if there is any rules-based explanation for the noted exceptions.

Answer: 
The Angry GM brings up this particular example in his article on Ability Checks. <https://theangrygm.com/being-in-flex-able/>

Since you’re asking this question, I highly recommend reading the full overview of ability checks, skills, and a seasoned review of the rules and some recommendations.

The short version is that he recommends asking for just the strength check first. But if the player has a reasoning for how Athletics (or any other skill) would apply in the particular circumstance, he would let the player add that.

Additionally, for reference, in The Angry GM’s free 5e module The Fall of Silverpine Watch he does not call out Athletics as a likely skill to work with forcing doors open.
I would allow either, on physical (real-world) grounds.

If you have the brute strength, then fine, use it, smash down the door on a plain Strength check.

If you have specific training for using and controlling your strength, then use that—a Strength (Athletics) check—to break down the door. Take advantage of the proficiency bonus you get from your training. Physically (in the real world) this would correspond to developing your core strength, not just arm or leg strength.