cant replicate this, works fine for me. make sure you use {NoAI:true}
model field is not necessary. when doing the same thing with carved pumpkin you get the expected result, the pumpkin appearing in your head, meaning this is indeed a bug concerning armors. perhaps there is some kind of difference regarding armors and pumpkins?
Fixed access to the Google drive, the uploaded attachment is very similar to the video in the drive
have you tried /kill?