"Crash" Item. These items can't be manually made on normal GamePlay without any others modifications. It was named "Client Items" since they are all from Hacked Client.
Save - tool bar is a thing but it not really possible to get that NBT tag which make your database corrupted and kick you out from the server.
There was a way to prevent Illegal NBT tags but It was removed after the Reset (NBI). Now, NBTs are limited but still don't cover up the whole thing. Like I would say it block all illegal NBTs from 1.8-1.12 but not 1.13+
The possible things may help you:
1. Your inventory must be cleared when you joined the server and before it kicks you out
Like when you join creative, it doesn't kick you out just yet, you have about 2 seconds staying there and your inventory must be cleared. Ask a Staff for inventory clear. Zquizle helped me with this once and maybe it would help.
2. Clear your database, could say that this is impossible to do for all staff members but you could try,
First, go on discord then join Pika discord. Then find MrFrenco and DM and state him this problem.
There was no precedent for this to happen but who knows.
My knowledge about Creative are limiteds so I hope this help. Asking people like
@June22 @Flat_Earth @Luppeey or
@UpperGround should help you get informations about Creative.
