This is caused by the time change due to
Daylight Savings time in most European countries.
Please note that this may cause the Daily Challenges timer to reset in specific circumstances related to when you have your Starting Time set. Visually, players would see the countdown expire for their next challenge, and then it will set itself back to 24 hour countdown for the next challenge, rather than offer the opportunity to start a new one.
If this happens:
A possible solution is to reduce the start time of the challenge by one hour, then you could immediately start a challenge again.
We are in any case working on a solution for this so that the next time the time is adjusted, this no longer occurs. Apologies for the inconvenience this is causing you in the meantime.