I saw a lot of tooltips saying "astral essence", when it's magic essence, like here : https://imgur.com/a/Yhtt0C8
And so, the DE profit is very wrong.

Maybe i saw the problem with some other kind of essences (not sure about that, i'll update the bug report if i see any).

Hey, did you actually disenchant it or just check on wowhead? it does say magic essence there but the item level (28) aux is correct according to this: https://cdn.discordapp.com/attachments/617057935121448971/618514289552130078/unknown.png. Maybe wowhead is wrong?
Unfortunately can't find a cheap one right now to check.

I did the DE myself, i did not check wowhead.

Hm, googled a bit and it looks like this might be a bug in wow classic ...
Weapons seem to never disenchant into astral essences regardless of level.