Problem with Performance function in Rekordbox DJ

Hi. I have a monthly subscription to Rekordbox DJ. I use it with CDJ850. But I have 2 problems with it.

First, I use it during 6 or 7 hours nonstop in private events, but every time I have a problem with the software : during the mix, it suddenly crashed without any reasons... Yet, it work very well during 5 or 6 hours. After a crash, I'm forced to restart the software and sometimes my Macbook pro before the "Performance" function could rework. 

But finally, I found a second problem with it. Since the last crash, it's simply impossible to use the "Performance" function. I can see this option in the top right of the screen, and I can switch between Performance and Export, but Performance don't work at all, with any CDJ's... However, I checked several times that my licence is still valid. And I also updated to Rekordbox 4.1.0 but nothing has changed. I have access to Export and Performance functions, but Performance is still unusable. 

Excuse my english, I'm french so... I hope you to have a solution for me. 

Cordially.