I don't know if this will help but I have had a similar problem with my 93 850. I parked it on a steep hill (my driveway) with the nose up. It cranked and would not start. I pushed it into the garage and tried again the next morning. I had to let it crank for about 20 seconds with a battery charger on jump mode. The cranking got faster and faster and it eventually started.
Over the past two years, I have noticed that if I turn on the car and move it to the garage for example then leave it off and don't start it for a few days; the car does the same thing. Battery is good etc etc but the pressure in the fuel system is gone and I have to turn the car over for up to a minute to get repressurized. I assume there must be some type of pressure release.
Good luck.
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