@ARom The scrambled graphics sometimes happen if there is no correct audio driver selected in Kontakt in standalone. Open Kontakt in standalone and choose an ASIO driver if you're on PC or a Core Audio driver if you're on Mac.
About Choir Omnia and FL Studio, I suspect this is related to this bug here: Kontakt 7 crashes in Fl Studio 21 when changing presets (KT-8739)
The bug should be fixed in the next Kontakt update. Until then, you can find an older version of Kontakt in the thread if needed.
For the Jade Evolution, did you try clicking on the '!' button inside Kontakt?
Try it, maybe it will refresh the library.
As for the Choir Omnia, maybe @Jeremy_NI can help...