I've seen the same thing happen with spell effects like Spirit Guardians. Either the caster will want to roll the damage on their turn, or the DM will forget to apply it when creatures start their turn in it.The thing I mess up on regularly are monster effects that happen on the players' turns. . . I keep wanting them to all happen on the monster's turn, but that gets just as confusing. So recently, a troll variant I was running had a gibbering confusion effect on anyone entering into or starting their turn within 20' of it. I kept wanting to force people to make saves on the troll's turn when he got within 20' of them and that led to actual confusion within a round.
While I understand 5E's attempt to make this kind of thing consistent, my brain keeps wanting for a monster's effect to be checked on in the monster's turn - because as DM it is easier for me remember that way. Except half the time I ask PCs to also make the saves on their own turn when they move into the radius.