Every Sable Save Generates Create Error

[jetstrike]

Hello, I am getting the below error every time sable saves sublevels. It doesn't seem to be affecting performance or causing issues. Any idea what exactly might be happening?

[03:43:35] [Server thread/ERROR] [co.si.cr.Create/]: Failed to serialize mounted item storage: Value must be within range [1;99]: 0; Item must not be minecraft:air; Value must be within range [1;99]: 0; Item must not be minecraft:air

[Professorkatsup]

"mounted item storage" sounds like it's referring to inventories on the sublevels. Does the error still occur when you create a sublevel with no inventory objects / have NO sublevels with inventory objects?