There is a known graphics bug where if anything else is also happening, like a regular crate being delivered or a clone chamber finishing, then the animation for the race having ended and your rewards does not show up. You still do get the rewards though. It's just that the animation for it is missing.
If you want to make sure to see the animation, try to completely shut down the app shortly before the race ends, and start it again after the race has ended. The "Race has ended" message should appear, and you should be seeing the animation for the rewards you got.
a month ago
I don't know, sorry.
What you could do to make sure that you got the rewards is to take screenshots of your main screen (for the credits and the diamonds) and of your units (for the cards).