Using the mid game / journey save feature on the PS5 native version (where you pause and press triangle) only works four times during the route (only tried on Boston), then any further attempts seem to corrupt the file and you get error message CE-100027-0 which doesn’t let you save again. You can complete the scenario though
I have encountered the same problem on the Boston route on the PS5 native version. The other routes don’t seem to have this problem.
It happens on several routes. Sometimes immediately at the first save but sometimes also after several successfull saves.
I had the same issue today on Dresden. I've had it on some other routes too like South Eastern High Speed.