Not_PreBool — logical NOT

NOT Boolean — logical NOT (invert boolean)

Negate_Vector — negate a vector (flip direction)

Less (float) — A < B

NotEqual_FloatFloat — check if A not equal to B

BooleanAND — logical AND

OR=BooleanOR, NOT=Not_PreBool, XOR=BooleanXOR

OR Boolean — logical OR of two booleans

string

string

Calling a function that doesn't exist on the target object

Why: You're calling '{fn}' on an object that doesn't have that function. The function may have been deleted, renamed, or moved to a different class. UE5 can't bind the call at compile time. Fix: Check the target pin's type. Search the Content Browser for the actual class name + look for '{fn}' in its functions. If found, drag a fresh reference and use the proper context menu Call Function path. If gone, find a replacement function or use an Interface call.

Two Blueprints reference each other in a way that can't compile

Why: '{a}' includes '{b}' as a hard reference, AND '{b}' includes '{a}' as a hard reference. UE5 can't compile either one first without the other already being compiled. Fix: Break the cycle by making ONE side use a SOFT reference (TSoftObjectPtr). Pick the side that doesn't need {b} immediately at construction — change the variable type to 'Soft Object Reference' instead of 'Object Reference'. Use Load Asset to resolve it at runtime.