Windows 10
Finale 25.4.1.152

1. Create any score (I just reproduced this with the Jazz Band template)
2. Add Kontakt to an unused VST bank
3. Add an instrument in that Kontakt instance
4. Use an expression to change the Channel of one of the instruments to that of the instrument you just added to Kontakt
5. Change an instrument via the Instrument List, or use the Change Instrument tool
6. Kontakt is removed from the VST bank and any changes made to the VST instrument are lost

Kontakt should remain, since one of the instruments depends on it (but even if it didn't, Finale still shouldn't be removing VSTs that I explicitly added).