ios – [ setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key

I’ve been getting the error message “[<UICollectionViewCell 0x14fd06a80> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key” for an image attached to a custom cell in a UICollectionView.
The cell’s IBoutlets are correctly linked up in the interface editor. There are no warning icons next to them.
I’m not quite sure whats going on.

Here’s the code for the custom cell:

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN


@interface CollectionViewCell : UICollectionViewCell
@property (nonatomic, weak) IBOutlet UILabel *maskName3;
@property (nonatomic, weak) IBOutlet UIImageView *maskImage;

@end

NS_ASSUME_NONNULL_END

Here’s what I’ve got in the interface builder: