I took off all my season characters gear including outfits, all wearable items, etc and also my chenga tome (which I had just used to quest to 61) and then used season time piece to switch places with another character.  I spent some skillpoints on the new character before getting booted for server downtime.

I logged on to the previous season character to find my chenga tome had been replaced by the elion tome. Never even had an elion tome on that character....

The black spirit gives every character an Elion tome.  Your original character should still have the Elion tome.

Every character can at level 53 do the Chenga quest to convert the Elion tome into a Chenga tome.  

I've had my Chenga tome disapear also with support saying that they "could not find the Chenga - Sherekhan Tome of Wisdom within your character's items, deleted items, inventory, or storage." I have zero idea where my Chenga tome went. I could have sworn that I moved it to a guardian I was playing last season but it only has the Adventures Tome on it. I'm starting to think something similar must have happened to mine.