Another example for the devs.
This just happened to my son yesterday.
Details:
Nintendo Switch (v1.18.2)
Crossing from nether to overworld
Lost all items, couldn't find them anywhere and lost XP as well
Normal sized portal
The loading screen took unusually long
He suffocated
The Totem Of Undying didn't save him
Thoughts:
Playing today my son noticed something odd when he was in a portal in the Nether he dropped a piece of glass and it transported to the Overworld on its own. Not sure if that's related or not he just didn't know if that was a normal thing occurrence.
I'm coming back to update after my son found something useful on the following bug:
MCPE-90769
In short, my son was able to recover his items by visiting the coordinates of the nether portal in the nether itself. All of his stuff was there and so was his XP. Even after almost 2 months of regular playing.