[MC-195568] Minecraft says "Reload failed, keeping old data"

MC-186468 (MC-186468) has the same issue, but it is in 1.16 Pre-Release 1 and snapshot 20w22a.

If I try to disable/enable [vanilla] built-in datapack, it says "Reload failed, keeping old data", no matter how I try to reload again.

Environment

Java Version

What's the bug?

that you cant disable vanilla datapack

This Works as Intended. You can't disable it.

Anthony Cicinelli, it doesnt. in older versions, you could disable it, and i didnt see any snapshot bugfixes / features about this.

And tryashtar, how can i fix it? the post doesnt say anything about it.