Just to dispel any perception that this issue isn't that big of a deal, I still deal with people running into this and reporting our Graves data pack not working because of it nearly daily. It's been driving me crazy for months now and makes giving technical support for our data packs significantly more time-consuming.

This is likely an issue in Spigot and Paper. EssentialsX is using the standard API to cancel drops (items not loot tables PlayerDeathEvent#getDrops#clear) and set the player to keep inventory (PlayerDeathEvent#setKeepInventory). I would try opening an issue with either Spigot or Paper because the only thing I would be able to do from the EssX side is manually triggering a loot table drop. Looking at the server code it looks like this was a previous issue with spigot that appears to have resurfaced.

@JRoy From the documentation on getDrops:

This appears to be generic to all entities (EntityDeathEvent), not just players. So if anything, it was originally meant for entity loot tables rather than player inventories. And see the description of the method--clearly, this intentionally includes drops from loot tables, and I'm sure countless plugins rely on it doing so. If I were to submit an upstream bug for this, it would be closed as Works As Intended. If that's the case, there's nothing strictly wrong with this method; EssentialsX merely misuses it.

@JRoy From the documentation on getDrops:

This appears to be generic to all entities (EntityDeathEvent), not just players. So if anything, it was originally meant for entity loot tables rather than player inventories. And see the description of the method--clearly, this intentionally includes drops from loot tables, and I'm sure countless plugins rely on it doing so. If I were to submit an upstream bug for this, it would be closed as Works As Intended.

No it wouldn't since there is no way to distinguish which drops are from a loot table or not.

That doesn't mean the getDrops method has a bug. Again, from the documentation, its intention is to include loot table drops. I won't submit an issue which will be closed as WAI directly based on the documentation.

If a data pack (Graves) can distinguish which drops are from loot tables and which drops are from the player inventory, surely a plugin (EssentialsX) can too.

That doesn't mean the getDrops method has a bug. Again, from the documentation, its intention is to include loot table drops.

I personally would maintain that's unexpected behavior since not even keep inventory in vanilla cancels those drops, however Paper would need to add some method to not cancel them if we were to get this fixed. Otherwise there's nothing I can do from the Essentials side

If a data pack (Graves) can distinguish which drops are from loot tables and which drops are from the player inventory, surely a plugin (EssentialsX) can too.

please point me in the direction of this api (there isn't one)

I personally would maintain that's unexpected behavior since not even keep inventory in vanilla cancels those drops, however Paper would need to add some method to not cancel them if we were to get this fixed. Otherwise there's nothing I can do from the Essentials side

I again emphasize that recreating keepInventory is not strictly the purpose of that method. Based on its description, EssentialsX misuses it for that purpose. Just because Spigot's API doesn't offer a feature doesn't mean an existing API has a bug. A plugin must work within the limitations of the plugin API.

please point me in the direction of this api (there isn't one)

There's no API for this in data packs either. You can distinguish it by checking whether the items were actually in the inventory before the player died. This should be even easier for plugins to check than data packs. I can give more details if you'd like.

I personally would maintain that's unexpected behavior since not even keep inventory in vanilla cancels those drops, however Paper would need to add some method to not cancel them if we were to get this fixed. Otherwise there's nothing I can do from the Essentials side

I again emphasize that recreating keepInventory is not strictly the purpose of that method. Based on its description, EssentialsX misuses it for that purpose. Just because Spigot's API doesn't offer a feature doesn't mean an existing API has a bug. A plugin must work within the limitations of the plugin API.

please point me in the direction of this api (there isn't one)

There's no API for this in data packs either. You can distinguish it by checking whether the items were actually in the inventory before the player died. This should be even easier for plugins to check than data packs. I can give more details if you'd like.

That actually could work, despite it being kind of a hack. Will look into this.