This is a known issue that we are currently investigating and we are hoping to fix it in a future update.
This is only a visual/display error, rest assured that you have actually claimed the rewards associated with the Play for X hours challenges even though the progress gauge is stuck.
Once we have resolved this bug, they will appear in the "Completed" challenges section as they're supposed to be.
For your information, there are 10 different stages for this challenge: 1 - 3 - 5 - 7 - 10 - 15 - 25 - 40 - 60 - 80
Once you have completed a stage, the next one will suddenly appear so you can complete it. When experiencing the bug causing the progress bar to be stuck, you will see that you have actually already unlocked the next stage(s).
We hope this helps and we thank you for playing F1® Mobile Racing!