Failed to load Outer for resource on opening a persistent level

For the past few weeks, I am getting these Failed to load Outer warnings when opening a specific persistent level in my project. I tried troubleshooting it myself to no avail, but was able to narrow down the list of culprits.

Here’s an overview of what’s going on:

  • A persistent level in the game includes a number of streaming levels.
  • There are NPC actors in some of the streaming levels. These use an ID parameter to load the necessary data to a struct (appearance, name, etc.) from the specified data table in construction script.
  • Among other things, data table for characters also includes links to ability classes of the characters. Note that specific actors in the level (the NPCs) do not actually do anything with these abilities.
  • After a number of tests, it seems the warnings only appear when an NPC actor in one of the streaming level has specific abilities in their struct. The abilities themselves work fine in the game, there are no compiler errors or warnings.
  • The warnings also appear only once per editor launch: opening the persistent level, then reopening it again without closing the editor does not cause the warnings to reappear.
  • The warnings do not appear if I open the streaming level with the culprit NPC actor directly.
  • Removing the abilities for which the warnings appear from the data table, then restarting the editor, does not help: the warnings for abilities removed still appear (something might be getting cached?). However, creating a fresh ID entry in the data table without these abilities, but otherwise similar to the original NPC ID, causes the warnings to disappear on next editor reload as long as the new ID is used.
  • The warnings also appear when packaging the game. They don’t seem to otherwise affect the process, however.

Of course, I also tried all the solutions I could find in previous answerhub threads on this topic, to no effect. I am at my wit’s end with this. As mentioned above, other than the warnings appearing, there seems to be no effect on the game. What exactly do these warnings mean? Should I even be worried?