Notion 4 & Play works, works not (after saving) why?

Hi there,
using Notion 4 and Play 4, both latest version. Using a quite big orcehstra setup up to 30 tracks), using severals sounds of integrated EWQL Orchestra, PLAY, Mirsolav Philharmonic, Notion instruments. Works quite fine, but again and again, since weeks, after saving the *.notion files after changes (for many many 100 times), when reopening it, there are no EWQL Orchestra or PLAY sounds.
Mixer - VST Instruments - VTS Manager says that play_VST_x64 is enabled.
But no sound.
I can open older versions of my project in a second surface, there it works.
I have to copy all the notes into the clipboard and copy it to the working notion project. but after saving it and reopening it, the sounds are missing so it is an endless story.
Any clue why?
using Notion 4 and Play 4, both latest version. Using a quite big orcehstra setup up to 30 tracks), using severals sounds of integrated EWQL Orchestra, PLAY, Mirsolav Philharmonic, Notion instruments. Works quite fine, but again and again, since weeks, after saving the *.notion files after changes (for many many 100 times), when reopening it, there are no EWQL Orchestra or PLAY sounds.
Mixer - VST Instruments - VTS Manager says that play_VST_x64 is enabled.
But no sound.
I can open older versions of my project in a second surface, there it works.
I have to copy all the notes into the clipboard and copy it to the working notion project. but after saving it and reopening it, the sounds are missing so it is an endless story.
Any clue why?