From the article:

Over the last years working with Seafile Ltd. has proven more and more difficult. Our cooperation now has reached a point where we can no longer in good conscience develop a software together.

Our goal at Seafile GmbH is and has always been to provide a stable and reliable product for our customers and the Open Source community. We have been disagreeing for a long time with

- the current development race,

- erratic changes of public plans,

- beta testing on paying customers,

- removal of features without proper prior notification or migration plans and

- disrespect towards data privacy when it comes to German or European law.

(that last bit is surprising...)