I am playing a game of Planechase, the current plane is Jund. I control three Agent of Fates and my opponent controls an Imposing Sovereign. I cast an Erebos, god of the Dead. When it resolves I choose to apply Devour first and sac all three Agents. Does Erebos enter the battlefield tapped?

There is this article that says it does, but it doesn't give any reference to the CR.

614.12 says “…taking into account replacement effects that have already modified how it enters the battlefield”
616.1e says “Once the chosen effect has been applied…”
Both of these imply that you apply the effects one after another. This would then mean that after applying Devour Erebos isn't a creature anymore and the Sovereign effect wouldn't apply to it. I.e. Erebos enters the battlefield untapped.
Other judges told me, that “apply” doesn't mean “do what the effect says” but only “put it onto a list of effects that we need to do as the next item” i.e. you first make a list of all replacement effects and only then all happen.
If that were the case the second example of 616.1e wouldn't work as described though.
The example is “Essence of the Wild reads “Creatures you control enter the battlefield as a copy of Essence of the Wild.” A player who controls Essence of the Wild casts Rusted Sentinel, which normally enters the battlefield tapped. As it enters the battlefield, the copy effect from Essence of the Wild is applied first. As a result, it no longer has the ability that causes it to enter the battlefield tapped. Rusted Sentinel will enter the battlefield as an untapped copy of Essence of the Wild.”
Here the copy effect clearly is actually applied wich then leads to the creature entering the battlefield untapped.

What is the correct answer and why?

The correct answer is the one the article described. As those other judges told you, to “apply” a replacement effect is not to perform the actions it describes, but instead to modify the set of instructions you're about to carry out.

The example in 616.1e you cite works as it does because when you're applying replacements that affect how an object is entering the battlefield, the way you determine which effects apply and how they apply is by checking what the object would look like on the battlefield, and during this process you take into account replacement effects that have already modified the event. (This process is laid out in CR614.12.)