Vanilla - Prison server. I was mindlessly mining in the S-mine in the prison server. I noticed when I looked back at the screen, I was lagging as the blocks around me were not breaking so I decided to relog expecting to return to normal and continue the grind. Upon return, my pickaxe was missing. Note I had toggled locked the pick into the first slot in the hotbar.

What I expected to happen was...:
Return into S-mine and continue as normal.

What actually happened was...:
Returned to S-mine and my pick with approximately 900k blocks broken and several dozen upgrades invested into it went missing.

Steps to Reproduce:
N/A, unsure on how to reproduce lag in this instance.