HackIM 2020 was an incredibly hard CTF, to the extent both members of our team were only able to solve a single challenge combined. The CTF recieved criticism for a couple of things (among others):
Some hints had been released after given challenges had been already solved at least once, making it unfair towards the teams that solved the given challenge without them. On top of this, some hints were only disclosed in Discord, which by the way, used far too many un-needed pings.
This is directly lifted from a comment on the CTFTime event page: "Releasing an n-day in Firefox as a 36h challenge was a bit too much as well, while no direction where to look was provided. People had understandable concerns about whether the admins had a working proof of concept in the first place. [Not] releasing the solution because the challenge was not solved is also unfair to teams that tried to solve the challenge and will maybe never learn what the solution was. At the same time, I am not sure whether releasing the [proof of concept] is a good idea since it was a 0day from the same version of Firefox (v72)."
Personally, I (Tom) did not think especially highly of HackIM as a CTF, however I did very much enjoy the Dora challenge that I did complete.