[BUG] C6 does not notify about missing plugins

As I have lots of old projects I noticed that when opening SX2 / SX3 project in C6, I don’t get any error message about missing plugins at all (although when checking Plug-in information via Menu, I can see them being Missing). If I save such a project afterward in C6 and re-open it, now I do get the “missing plugins” error window.
Strangely enough there is no problem with SX 1 projects e.g. I correctly get the “missing plugins” message when opening SX 1 project in C6.

I already contacted Steinberg support and got confirmation from Jan Hendrik Peters that he “will report this issue to the respective departments” so hopefully it will be fixed eventually.

I am surprised that nobody else noticed this…