In almost every instance we see this occurring, it's an issue related to swapping a driver on your team rather than something happening at random or the system failing. Here's why:
In order to utilize a talent driver, you must have all 6 positions on your roster filled. If you have all 6 filled and have a talent driver selected, but then make a change by removing a driver and adding another one, your talent driver will deselect itself because you have temporarily moved below the threshold of having all 6 positions filled.
There are plenty of notifications in place to help you avoid this mistake. League cards are highlighted with a blue bar with the message "incomplete team" if you are missing positions or a talent driver is not selected. Additionally, a large red bar will appear on the "my team" screen warning you that you have not selected a talent driver. Lastly, if you have notifications enabled, you will receive one 24 and 4 hours prior to lockdown reminding you to complete your team.
Lastly, talent drivers are only eligible based on CURRENT driver salary. If you select a talent driver that is below the salary threshold but they move above the salary threshold due to good performance, you must select a new talent driver that is under the threshold.