Packaging failed due to Assertion Failed ClassData

I’ve been trying to package my game but it keeps saying critical error. I was able to package it properly yesterday, and barely even touched anything today. I literally have no idea what’s going on, and I don’t have a recent backup to be able to revert to. What can I do??

UATHelper: Packaging (Windows (64-bit)): LogWindows: Error: === Critical error: ===
UATHelper: Packaging (Windows (64-bit)): LogWindows: Error:
UATHelper: Packaging (Windows (64-bit)): LogWindows: Error: Assertion failed: ClassData [File:D:/Build/++UE4/Sync/Engine/Source/Programs/UnrealHeaderTool/Private/CodeGenerator.cpp] [Line: 2665]
UATHelper: Packaging (Windows (64-bit)): LogWindows: Error:
UATHelper: Packaging (Windows (64-bit)): LogWindows: Error:
UATHelper: Packaging (Windows (64-bit)): LogWindows: Error:
UATHelper: Packaging (Windows (64-bit)): LogWindows: Error:
PackagingResults: Error: === Critical error: ===
PackagingResults: Error: Assertion failed: ClassData [File:D:/Build/++UE4/Sync/Engine/Source/Programs/UnrealHeaderTool/Private/CodeGenerator.cpp] [Line: 2665]