Killed in portal from fall damage lost everything

We entered nether portal in our overworld (shashas) to go to the nether. First person (BitterHotMom747) went thru fine. Second player (MrKidMarco) walked into portal and Screen started warping showing going to Nether. Couldn't see anything other than warping screen but could hear he was taking damage. Never came out of portal. Screen finally popped up saying you died from fall damage. We looked and nothing was wrong with portal. Nothing was left scattered around portal. Lost everything in inventory. Dug under and around portal to see if inventory was there and can't find anywhere. Don't understand how going thru portal kills you with fall damage. After respawn he tried to go thru again and it killed him again with fall damage. After respawn again tried a third time and finally worked correctly. Can't get it to repeat a third time. Other player had no issue. How do we get inventory back and prevent portal from killing player?