Common Blueprint mistakes and how to fix them

MISTAKE 1: Calling GetAllActorsOfClass every Tick. FIX: Cache results in BeginPlay or use delegates/tags instead. MISTAKE 2: Not checking IsValid before using object references. FIX: Always IsValid → Branch → Is Valid before dereferencing. MISTAKE 3: Using hard references to large assets in variables. FIX: Use Soft Object References + AsyncLoadAsset. MISTAKE 4: Tick enabled on many actors doing heavy work. FIX: SetActorTickInterval(0.1) for non-critical logic, or use Timers. MISTAKE 5: Casting to specific class without checking IsValid first. FIX: CastTo has 'Cast Failed' output — always handle it. MISTAKE 6: Modifying array elements by getting then setting a copy. FIX: Use 'Array Set' with index to modify in-place. MISTAKE 7: Creating widget every time it's shown. FIX: Create once → cache reference → show/hide with SetVisibility or Add/RemoveFromParent.

Compile failed with {count} errors — open the Errors panel

Why: UE5's main message just says how many errors occurred, not what they are. The actual errors live in the Errors panel. Fix: Open the Blueprint editor. Click Window menu → Errors Panel. Expand each entry to see specific node locations. Use the Errors panel's hyperlinks to jump straight to the broken nodes. Fix from top to bottom — often one fix cascades to clear several others.

ApplyDamage — deal damage to a target actor

UGameplayStatics::ApplyDamage. Triggers EventAnyDamage on target.

Asset was saved with a different UE5 version

Why: This asset was saved with UE {ver}, but you're opening it with a different version. Compile differences between versions can cause errors. Fix: Best: open in the original UE {ver} version, do whatever migration is needed (Project menu → Convert In-Place), then re-open in your current version. If you don't have UE {ver}: open + save the asset, then re-compile. If errors persist, the underlying API may have changed between versions — check UE5 release notes for breaking changes.

Function name collision with parent class or duplicate

Why: You created a function named '{fn}' that conflicts with one already defined — either by the parent class (which you should Override instead) or another function in this same Blueprint. Fix: If you meant to override a parent function: delete your function, then right-click in My Blueprint → Override Function → pick '{fn}' from the list. If you meant a separate function: rename yours to something unique (e.g. '{fn}_Custom').

Not_PreBool — logical NOT

ApplyPointDamage — deal point damage with hit info

BooleanAND — logical AND

OR=BooleanOR, NOT=Not_PreBool, XOR=BooleanXOR

EventAnyDamage — receive any type of damage

Event AnyDamage — fires when this actor receives damage