After a certain playing time triggering a unique stunt jump will cause the camera to freeze only leaving you the option to stop playing or use a code to accelerate time. Using the latter seems to progressively corrupt your savegames.

Whatever you choose the unique stunts are a serious problem after a certain time. This mod fixes it by preventing you from redoing the unique jumps.

You can still complete the multistorey mayhem challenge however.

Setup

Copy and paste GTA3NoMoreUniqueSstunts.ipl in your GTA 3/Data/Maps folder.
go back to your GTA 3/Data folder,
open GTA3.dat
go the # Scene information section
at the bottom add the following line
IPL DATA\MAPS\GTA3NoMoreUniqueStunts.ipl
Voilà!

My other mods

GTA 3
Fast unsinking Liberty cars
Improved Shoreside Vale roads
Spring weather
The invincible gangster killer

GTA Vice City
Vicious speed unsinkable vehicle