Errors while packaging plugin, even though the project can be compiled and packaged without errors?!

Hey! So I’m a little bit confused by this.

When I go to the Plugins window and try to package my plugin for distribution, I get a bunch of compile errors. This is a C++ code plugin. The build process starts, building UE4Project goes through, but when it comes to building UE4Game, a lot of compile errors pop up. Mainly missing types.

How come that I cannot package the plugin while I can package the whole project (debug and shipping are all fine) without any issues? Is this normal behaviour? Should I just sit down and include all missing headers?

Few examples:

UATHelper: Package Plugin Task (Windows):   Building UE4Game...
UATHelper: Package Plugin Task (Windows):   Using Visual Studio 2017 14.16.27044 toolchain (C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023) and Windows 10.0.17763.0 SDK (C:\Program Files (x86)\Windows Kits\10).
UATHelper: Package Plugin Task (Windows):   Building 4 actions with 16 processes...
UATHelper: Package Plugin Task (Windows):     [1/4] Module.Kronos.gen.3_of_3.cpp
UATHelper: Package Plugin Task (Windows):     C:\Users\Balogh Roland\Desktop\Kronos\HostProject\Plugins\Kronos\Source\Kronos/Public/KronosTypes.h(245): error C2653: 'FPackageName': is not a class or namespace name
UATHelper: Package Plugin Task (Windows):     C:\Users\Balogh Roland\Desktop\Kronos\HostProject\Plugins\Kronos\Source\Kronos/Public/KronosTypes.h(245): error C3861: 'ObjectPathToPackageName': identifier not found
UATHelper: Package Plugin Task (Windows):     C:\Users\Balogh Roland\Desktop\Kronos\HostProject\Plugins\Kronos\Source\Kronos/Public/KronosTypes.h(246): error C2065: 'GEngine': undeclared identifier
UATHelper: Package Plugin Task (Windows):     C:\Users\Balogh Roland\Desktop\Kronos\HostProject\Plugins\Kronos\Source\Kronos/Public/KronosTypes.h(1166): error C3646: 'TimerHandle_ReservationTimeout': unknown override specifier
UATHelper: Package Plugin Task (Windows):     C:\Users\Balogh Roland\Desktop\Kronos\HostProject\Plugins\Kronos\Source\Kronos/Public/KronosTypes.h(1166): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int