The fact he was elected to the Citrix board on June 22 with the largest number of votes for and fewest against of the nine board members and resigned on July 7 does say "abrupt". One observer said most signs indicated Tatarinov did a good job.
His LinkedIn profile describes his Citrix experience this way "Introduced new vision & strategy and dramatically advanced corporate culture focusing on innovation and transformation to the Cloud." Tatarinov was replaced by CFO and COO David J. Henshal, with the company saying it has adopted a new direction. Tatarinov officially received $22,373,000 in compensation for fiscal 2016, including a base salary of $1 million and stock awards of $18,254,249. Normally, equity compensation is restricted and vests over time, typically with each tranch vesting on the anniversary of the exec's hiring. My quick perusal of SEC documents did not find the terms of Tatarinov's departure, other than his concurrent resignation from the Citrix board of directors.