I bought the necromancer pack. Some of the season 24 items were deleted from the mail when it was active. Please check
Let me guess. Your etherial items.
There were too many items to confuse. I don’t know exactly what is missing
At the end of Season 24, all ethereal weapons were deleted, exactly as the blog said would happen.
When you say items are missing are you talking about items you found during the season or items from the Necromancer pack itself?
If thats the case then nothing is missing as the pack does not give you any items, just the new characters, wings, banners and a pet. All of which are account bound and cannot vanish.
Yeah right!
It’s a good idea to clean up as much as possible towards the end of a season. Both in your seasonal and non seasonal stash. If you also fill up your seasonal heroes’ inventories before season end you’ll have less in the mail to sort through.
The stones and items I collected during the season are missing. I consider that you have a sense of humor when you talk about ethereal items 
Have you checked the mail ikon in the lower left corner of the game screen?
The keystones are in the materials tab when you open your inventory. Your season keys are added to the non season amount just like the other materials.
They did for me too. None of the wizard items appeared in mail. I don’t care as they are no better than my non season anyway