Why does the Buckets only work when it feels like it?

I do a race and it works fine (3 Groups) so next one I set up (4 Groups) I find only one car in the race and that is me. I had added the Dodge/Valiant Charger and then figured it is locked so might not work and quit out then tried using an available car in its place. I closed the app and reopened just in case it was hanging on the old settings but nope after multiple attempts for 1/2 hour I still only have my car in the race. Everything is set to correct number of cars etc. I have given up on it now but if anyone has a clue please enlighten me thanks