Building Mod Issue

Check the tracker rules:

When possible, attach your MCreator workspace (or even better a minimal example workspace required to reproduce the bug), game logs (full logs, do not crop them, in text format, not screenshots of logs) from the Console tab or terminal and steps to reproduce the bug in your workspace. If logs are long, use service such as Pastebin to host the log and provide the link to the log from the ticket. Please specify which mod elements to check in your workspace too, if applicable.

This guide might help too: https://www.youtube.com/watch?v=UzNvogqbHDg

Leave a comment once the ticket is fixed.

I suggest you try updating BlockBench and exporting the armor model again and importing it again.

Please report back if this fixed the issue.