Behind the paywall, unfortunately, but Cultaholic reports on it here:

All Elite Wrestling’s return to Arthur Ashe Stadium for Grand Slam III unfortunately produced a moment of controversy, with AEW International Champion Jon Moxley suffering a concussion early into his match with Rey Fenix and being allowed to continue to compete.

Whilst it was reported that those at ringside were unaware that Moxley had suffered an injury during the bout, Fightful Select reports that there was a lot of heat on referee Rick Knox, with Knox’s performance justifiably criticised online.

The report states that whilst Knox is liked in AEW, this wasn’t the first time his judgment has been called into question, with Knox botching a three count and allowing Moxley to take two Fire Thunder Drivers at Grand Slam to the ire of Mox and viewers worldwide. Knox has previously been involved in officiating where a wrestler has not been properly protected, with Knox having missed what looked to be an apparent knockout on Alex Reynolds during a Dynamite match in 2020.

Moxley is believed to have walked out of Grand Slam on his own two feet, but was immediately checked upon by Tony Khan, and members of the Blackpool Combat Club. Moxley is believed to have suffered a concussion after landing hard on the outside of the ring when taking a Fenix plancha off the stage. Moxley called an audible to facilitate the title change.
https://cultaholic.com/posts/report-heavy-heat-on-rick-knox-following-aew-grand-slam