Computer AI at the Insane difficulty level has a few issues. Some of them are long pre-existing yet are still annoying as ever:
Human:
Sometimes, the AI gets stuck in the Tier 1 mode and doesn’t upgrade well into 1 hour + in-game or even longer: Computer (Normal) doesn't upgrade when playing as Human. It is definitely an AI script issue, it is still happening, and it is happening only with a Human faction. No other factions have this issue: Undead upgrades their tier the earliest, but Orc and Night Elf are pretty quick to upgrade and never get stuck in this Tier 1 mode that goes on forever as Human AI does.
https ://imgur.com/a/DwPDKbX
Night Elf:
Sometimes, newly trained heroes and land units that get out of the production buildings, get stuck in the trees. Now, I know that can happen with any faction, but all the other factions are cutting the trees down with workers, and so the units that are stuck in trees, will be set free eventually. In the case of Night Elf, however, the units will sit in their base for ages, possibly forever, and the AI is scripted in such a way, that it will either not move out of their main base with a whole massive army of theirs if it doesn’t include those stuck units, or if it does move, its combat power will be severely hindered, given that half of their army is stuck at their main base. Most of the time this happens when AI builds an Ancient of Lore in place of their collapsed gold mine at their starting base, but this can also happen with any building that is producing land units, such as Altar of Elders, that is built too close to the trees.
https ://imgur.com/a/RgitEZZ