EDIT: This is now the version of Graves on Vanilla Tweaks!

For support, you can ask in the data pack help channel on the Vanilla Tweaks Discord server: vanillatweaks.net/discord/

But here is the old description from before that was the case:

Problems with Vanilla Tweaks Graves:

• Sometimes your items just don't go into your grave.
  
• You can't prevent others from picking up your items when opening a grave.
• You can't configure grave robbing to be enabled.
• You can't tell who owns a given grave.
• Grave data is stored in floating minecart hoppers 300 blocks above the grave, where they can be reached via elytra & firework rockets. Pushing the minecart hoppers makes your grave dysfunctional. Opening them allows players to steal your items.
• The data pack is incompatible with any Players Drop Heads data pack, as the player head will drop into the grave instead of to the killer.
• Graves can't pick up XP.
• Pushing a grave with a piston makes it largely dysfunctional.
• Graves often spawn one block above the ground.
• The hitbox of a grave takes up 6 blocks when it only needs to take up 1.
• Sometimes graves randomly pick up rails, among other things.
• If two people die at the same time, only one grave gets all the items.
• If you crash or disconnect before dying, you never get to see your grave coordinates.
  
• If you change your username, you can no longer open any of your past graves.

I tried to fix ALL of the above issues.

Unique features of this Graves data pack:

• Retrieve your items and/or XP dropped on death from your grave by right-clicking it with an empty hand.
• Hold crouch when you right-click to make it so only you can pick up the items.
• If grave locating is enabled, enter "/trigger grave" to see the coordinates of your last unopened grave. If you open your last grave, it will display the location of your second-to-last grave, and so on.
• As an op, enter "/function graves:config" to configure whether grave robbing, graves collecting XP, and grave locating are enabled, or for an option to give yourself a grave key to forcibly open graves.
• Stand near a grave to display the nametag of the player who owns it above it.

Possible death scenarios:

• When you die in midair, your grave will spawn on the ground.
• When you die above or in water, your grave will sink to the bottom.
• When you die in lava, your grave will remain at the surface.
• When you die to the void, your grave will appear at y=1 with a grass block below it.
• When you die inside blocks, your grave will spawn on top.
• When you die in the same place as another grave, your grave will spawn above that one.

To uninstall, enter "/function graves:uninstall". This will disable Graves and reload your data packs, but it will not remove any graves placed in the world. To remove all graves currently loaded in the world, enter "/kill @e[​type=minecraft:armor_stand,tag=graves.marker]". After entering the uninstall command, you're good to remove the data pack file.