The FMC seems to be unstable. I was doing the tutorial flight two times, and it always crashed two times on this page:
To be more specific, when finishing entering the PMDG tutorial PDF flight plan KPDX MINNE5 FAMUK Q3 FOWND MLBEC BDEGA3 and ILS28R to KSFO.
Trying to enter the last entries FOWNED MLBEC … brings the sim to a stuttering crackling end back to the desktop.
The second problem is, the airplane always loads with both hydraulic systems with too low hydraulics fluid whenever random failures, or maintenance base failures are activated in the FMC:
But I don´t want to have realistic failures disabled!
No matter how often the maintenance is done, and all technical errors are cleared in the FMC - whenever the next flight is choosen it always starts with a hydraulic failure.
But luckily the 737 is equipped with wires and pulleys so having no hydraulics should not be such a big deal… 
edit:
Aha that happens on other versions of this plane too:
https://forum.pmdg.com/forum/main-forum/pmdg-737-ngxu-for-prepar3d-v4/29584-hyd-fluid-system-a-refill
By the way now I understand why all Boeings MUST be equipped with an ECAM till the end of 2022.
When there are system failures appearing (and I love that because that makes the flights really interesting, one has to switch off overheating pumps and take care of the machine and this and that…) - but in many cases I simple don´t know what failure it is.
In the Airbus there is an ECAM message saying exactly what´s wrong, and in the Boeing… there is… an illuminated master caution button.
(Of course when going in the FMC maintenance page one can read what failure it is - but what does a real pilot do when a failure occurs? Just a master caution button and some absolute basic announciator panel having a light bulb behind pre-defined words like “FLT CTR” or “ELEC”, but nothing else and no detailled informations.)