VST3 SDK samples buggy in FL Studio

[Reizo prime]

I'm trying to start writing my own VST3 plugins using only the standard VST SDK by Steinberg without any additional framework (like JUCE).
However, after I finally managed to get the included sample projects compiled properly (and validated by the also included 'validator') using them inside FL Studio is still kinda buggy in several ways:
- When loading the agin.vst3 the plugin window by FL Studio is way larger than the actual GUI of the plugin (making the window parts not used by the GUI transparent).
- The 'noteexpressionsynth.vst3' displays error messages saying "Access violation at address <some memory address> in module 'noteexpressionsynth.vst3'. Read of address FFFFFFFFFFFFFFFF." constandly and "Invalid editor window handle!" when trying to open the plugin window (while the GUI was still loaded, when opening the plugin for the first time).
- Most plugins display no GUI (which, of course, might also be, because they don't provide one).
- Also most plugins don't appear to do anything at all (which again might be just the nature of the plugin, that I do not comprehend).

So, is there a way to fix those issues, are they known or common, or FL Studio-specific?

I hoped to use the sample plugins as a template for getting started with writing my very own plugins but they don't seem really helpful when they don't work properly in the first place. Generally speaking, I could not find ANY introduction for developing vst plugins without any additional framework. Also the SDK documentation is rather poor for my, expectation. Thus, if there's any source you can provide I'd be really happy about that, too.

[mcpp]

Hi I found sometime that the plugins loads in ...