When is a plot-hole not a plot-hole? Most commenters would say when it's the product of a writer on the Internet nit-picking needlessly or someone fundamentally misunderstanding what a plot-hole is. Fundamentally though, the definition is simple: it's a gap in logic or in the story that requires something to fill it.
Most of the time, those explanations are added in-universe (if they ever come), thanks to sequels or deleted scenes or the creator explaining something sufficiently with the existing material. But the Wizarding World and JK Rowling are somewhat different. Because she's built an expanded universe governed by lore and libraries full of mythology, she's been able to add story details on to her primary texts with abandon for years.
Rowling has never been scared to answer fans. And on top of that Pottermore adds whole backstories and almost every character, artifact and spell has been fleshed out further since the books' release, meaning a significant number of things that initially APPEARED to be plotholes now are not.
Though there ARE plot-holes in the Harry Potter universe, some of them actually have entirely legitimate solutions - most of which have been confirmed by Rowling herself...
As established by the lore of the wizarding world, Thestrals can only be seen by people who have witnessed death. And yet Harry can only see Thestrals in this fifth year, despite having witnessed several deaths, particularly Cedric's, which happened JUST before Harry got onto the carriages that still appeared to be drawn by nothing.
JK Rowling has answered this one - apparently after being asked about it a lot. She says it's about actually processing the death rather than simply seeing it and also qualified that Harry didn't actually witness the deaths of his parents or Professor Quirell (he was too young and unconscious respectively).
For Cedric, she explains more in detail why it takes until book 5 for Harry to see them:
"Anyone who has suffered a bereavement knows that there is the immediate shock but that it takes a little while to appreciate fully that you will never see that person again. Until that had happened, I did not think that Harry could see the Thestrals. That means that when he goes back, he saw these spooky things. It set the tone for Phoenix, which is a much darker book."