It has been a year in which the GRU’s operations, from election hacking to novichok poisoning, have been uncovered and plastered on the front pages of western newspapers more often than the secretive military intelligence agency, or its Kremlin bosses, would like.

It was unsurprising, then, that news of the death of Igor Korobov, the agency’s head, should cause a flurry of speculation about its timing. Korobov, 62, died after a “long and difficult illness”, according to a short news item released by Russian agencies on Wednesday evening.

Rumours had surfaced in recent months that Korobov had been dressed down by Putin after a series of public failures by the agency, and subsequently fallen ill.

However, some in Moscow insisted there was nothing suspicious about the death and said Korobov had died after a long battle with cancer.

“He had been ill for some time. If you look at the recent pictures of him you can see very well that he was suffering. There is absolutely no suggestion of foul play here,” said a source in Moscow who knew Korobov personally, but asked not to be named because he was not authorised to discuss intelligence matters.

Sergei Kanev, the Russian journalist who has carried out much of the research into uncovering GRU operations in the past year, was a little less sure: “It was certainly well-timed cancer. He knew a lot about the GRU’s secret operations, including about the poisoning of the Skripals.”

However, a number of Russian media sources also claimed to have information that Korobov had been ill for some time. The independent newspaper Novaya Gazeta wrote that Korobov’s deputy, Igor Kostyukov, had basically been in charge of the agency since summer, with Korobov absent due to illness. Alexei Venediktov, the well-connected head of the liberal Ekho Moskvy radio station wrote on Twitter: “He really was seriously ill for a long time.”

According to his official biography, Korobov served in the Soviet army from 1973 and moved to the intelligence wing in 1985. He was appointed to head the agency in 2016 after the premature death of Igor Sergun, his predecessor. The GRU is the most secretive of Russia’s three intelligence agencies, and Korobov did not speak in public or give interviews and was rarely featured on Russian television.

The Kremlin released a short, factual statement confirming Korobov had died and saying that the president, Vladimir Putin, expressed his condolences to Korobov’s family. It was in notable contrast to a similar statement marking Sergun’s death in 2016, which praised his character at length and called him “a genuine military officer, an experienced and competent commander, a very brave man and a true patriot”.

Mark Galeotti, an expert on the Russian security services, described Korobov as “neither radical and revolutionary, nor problematic and incompetent”, saying he was overshadowed by Sergun, who had presided over a period in which the agency’s operational reach and prestige increased dramatically.

Over the past couple of years it has become clear that the GRU has not been ready for the age of data journalism and citizen detectives. Remarkable work by The Insider, a Russian news outlet, and the online sleuths of Bellingcat has pulled back the veil of secrecy from a number of GRU operations, which have included a failed coup attempt in Montenegro, involvement in the shooting down of a Malaysian Airlines jet over eastern Ukraine in 2014, and the poisoning of Sergei Skripal and his daughter in Salisbury earlier this year.

The latter has been particularly embarrassing for the agency, especially after the two main suspects went on the Kremlin’s television station, Russia Today, to deny they worked for the GRU and claim they were holidaying vitamin merchants. Bellingcat and the Insider later released detailed and convincing exposes of the men’s two real identities, and their ties to the GRU.

Sergei Naryshkin, the head of Russia’s SVR foreign intelligence agency, publicly called the Skripal operation “unprofessional”. His words were ostensibly meant as proof that the Skripal poisoning was a “crude provocation” by Britain, but as mounting evidence of Russian involvement was already in the public domain, it was hard not to read it as a stinging rebuke of the GRU’s operational standards.

Still, Galeotti said the idea that has sprung up over recent months about the GRU as bungling and incompetent was misjudged.

“The Kremlin has a much more wartime mentality, that if you’re expecting an agency to be out there and active and aggressive, some of them are going to get blown, occasionally,” he said.

At least publicly, Putin has remained staunchly supportive of the GRU. At a televised event celebrating the agency’s 100th anniversary earlier this month, he read through a list of sparkling military intelligence achievements without hinting at the recent GRU strife.

“As the commander in chief, I of course know your unique possibilities, particularly in carrying out special operations,” said Putin, and reminded those present that special disdain was held for those like Skripal: “There is no bigger shame than to betray your fatherland and your comrades.”

Galeotti said there will be clues as to whether the GRU will change or consolidate going forward when a permanent successor is chosen. “Either way, the intelligence campaign against the west will continue. That has nothing to do with who is in charge at the GRU, and everything to do with who is in charge in the Kremlin.”