It looks like from his birth to his death he was writing at least one thing every year. However there seems to only one noticeable gap between:
The Anniversary of the Lena Massacre (February 1913)
The Soviets of Workers’ and Soldiers’ Deputies (March 14, 1917)
Which is a huge four yeargap! Now this obviously coincided with the Russian Revolution and World War One but why would he stop writing just before World War 1 started instead of continuing to write about the war? And during the war wouldn't 'status updates' or something be important? So what was Stalin doing during this time which made it impossible to write when he managed under difficult circumstances before (and after) to publish at least something every year?
Stalin was in exile from 1913 to 1917, in a remote part of Siberia (Turukhansk). As Stephen Kotkin notes (I'm citing his Stalin, Volume I: Paradoxes of Power, 1878-1928 throughout), it "was the longest consecutive term of banishment he would serve, wallowing near the Arctic Circle right into 1917. (p. 152). Both Lenin and Trotsky wrote during this period, and the absence of anything from Stalin was noted by Trotsky (p. 153).
Kotkin suggests "extreme isolation," and notes that Stalin constantly asked for fellow Bolsheviks to send him books and other reading material, at one point even wanting to expand on his 1913 essay "Marxism and the National Question." An article was apparently written in early 1914, "On Cultural Autonomy," but it disappeared soon after and has never been recovered, while two other articles, "The National Movement in Its Historical Development" and "War and the National Movement" were mentioned in letters in 1916 to Kamenev (p. 153).
Kotin also notes that the dearth of writing by Stalin cannot just be explained by isolation. While in Turukhansk, Stalin spent time with Yakov Sverdlov, who would later play a major role with the Bolsheviks; Sverdlov managed to write articles while up there, so there is no reason Stalin couldn't have as well (p. 154). Stalin seemingly busied himself reading and engaging with locals, even fathering two sons with one of them (the first when the girl was only 13; the child died shortly after, and Stalin never acknowledged him, while the second survived). He was also drafted in 1916, but because of his physical ailments, he was disqualified (p. 155).
So overall, it seems that Stalin took a bit of a break during the time, and just lived life as a Siberian local would, fishing, trading with locals, and reading.