Glitched Autosave

Hello, I am a Minecraft player who got full diamond armor for the first time ever! (in survival)

However, next week when I was planning on going to the nether for the first time, I check my chests (I only have 2) and my inventory and there was no diamond armor! I am so frustrated with this glitched autosave and I want the devs to fix this issue as it is so frustrating. Anyways, if the devs are reading this issue, thank you for doing so and please fix this!