Flight-loading contretemps

For reasons unknown, once a flight is created and flown and saved, on attempting to use the flight a second time the flight loads up to 12% (exactly) and then the program stops responding.
No variable seems to be directly responsible. And if an identical flight is created again, the new flight loads perfectly. But if the new flight is saved and then reopened at a later session, 12% is the limit of loadup.
Nothing to do with the add-on aircraft evidently, but perhaps a result of the much-added add-on scenery.
Can anyone suggest why these created flights can only be flown once, then not at all after they have been saved?
Many thanks for any technical insights available.
All the best,
Lysander77
No variable seems to be directly responsible. And if an identical flight is created again, the new flight loads perfectly. But if the new flight is saved and then reopened at a later session, 12% is the limit of loadup.
Nothing to do with the add-on aircraft evidently, but perhaps a result of the much-added add-on scenery.
Can anyone suggest why these created flights can only be flown once, then not at all after they have been saved?
Many thanks for any technical insights available.
All the best,
Lysander77