Mods

I'm working on a mod (for a personal project of mine) that allows for the game to be controlled wirelessly through commands. It's a challenge for the game where the output from the game will be streamed to connected viewers. The audience may control the game's instance through commands. I currently have it so that the ingame character's movement may be controlled via commands as well as specifying which multiplayer server to join etc. however loading up a singleplayer world is ironically seemingly more tedious and I haven't been able to get far with that part. I would like to give the audience the opportunity to either choose to join a server and try controlling the game through commands only or choose to create or join a pre-existing singleplayer world. Naturally, checks will be made to ensure no one abuses this system and tries spamming servers with connection requests. 

Yes it seems the tile entity method #writeToNBT is acting the same way

Did you verify your tile entity was being saved? Or just the custom item?

I was not, I added it to all the places I change the data and it did not change the issue unfortunately. 

Are you calling markDirty on your tile entity whenever you change it's data?