Error after changing BP parent class: “OwnerClass should not be 'REINST_'!”

I have multiple “Enemy” blueprints that inherit from a “CombatAI“ parent class, which in turn is a child of the default “Character” class. After reparenting “CombatAI“ to a new “CustomCharacter” class, I’m getting the error message below.

Old class hierarchy: Character > CombatAI > Enemy

New class hierarchy: Character > CustomCharacter > CombatAI > Enemy

LogOutputDevice: Error: === Handled ensure: ===
LogOutputDevice: Error: Ensure condition failed: !FBlueprintCompileReinstancer::IsReinstClass(OwnerClass) [File:D:/Build/++UE4/Sync/Engine/Source/Editor/UnrealEd/Private/Kismet2/KismetReinstanceUtilities.cpp] [Line: 1763]
LogOutputDevice: Error: OwnerClass should not be 'REINST_'! This means that a REINST class was parented to another REINST class, causing unwanted recursion!
LogOutputDevice: Error: Stack: 
LogOutputDevice: Error: [Callstack] 0x00007ffd6e1c1769 UE4Editor-UnrealEd.dll!DispatchCheckVerify<bool,<lambda_787fa22efeea56ac530ee0812261dd56> >() [D:\Build\++UE4\Sync\Engine\Source\Runtime\Core\Public\Misc\AssertionMacros.h:164]
LogOutputDevice: Error: [Callstack] 0x00007ffd6d9d98e8 UE4Editor-UnrealEd.dll!FBlueprintCompileReinstancer::MoveCDOToNewClass() [D:\Build\++UE4\Sync\Engine\Source\Editor\UnrealEd\Private\Kismet2\KismetReinstanceUtilities.cpp:1763]

The error pops up seemingly at random when I edit any of the blueprints. I couldn’t find any way of deliberately reproducing the error, nor isolating which blueprint exactly is causing the issue.

I made a lot of deep-reaching changes before noticing the error, which makes it difficult to undo everything. Does anyone know what this error even means and how I can fix it? Web searches are giving me nothing related to my particular issue.