I just found that in S22 they have inverted the behaviour of a flag for GetAllAssets.
In R21 there existed a flag ASSETDATA_FLAG::MISSING.
From S22 onwards the functionality of this flag has been inverted and it is now called ASSETDATA_FLAG::NOMISSING.
The problem is that it sets the exact same bit.
So if you have a plugin that is compiled against R21 and your users use it in S22 then your code will not be getting the missing assets anymore, since this bit is set (if you use the MISSING flag) and it will now mean DO NOT get missing assets.
Compiling against the S22 SDK and removing the MISSING flag will fix your bugs if you have any.
Just something to watch out for if anyone is hearing of problems from your users relating to gather up assets. Mainly applies to people writing renderers and dealing with textures and materials.