Less than three years after the debt problems of state-controlled oil company Rosneft nearly crashed the rouble and the banking system with it, there are signs of stress again. This time, the biggest bank in the firing line is the very same bank that played a key role in the brush with crisis in 2014.

FK Otkrytie (pronounced Ot-KRIT-eeya) was Russia’s biggest privately-owned bank by assets at the start of the year, ranking only behind state-controlled Sberbank, VTB and Gazprombank. It now appears to be in serious trouble, after losing over 621 billion roubles ($10.5 billion) in a deposit run in July amid concerns over possible hidden losses on its balance sheet.

The news site RBC reported that Otkrytie lost some 30% of its external funding last month. It plugged the gap by asking the Central Bank of Russia, its lender of last resort, for an extra 333 billion roubles in funding and by shrinking its corporate loan book by an eye-watering 38%.

Rumors about Otkrytie have been swirling since ACRA, a local ratings agency, commented on the “low quality of its loan portfolio” at the start of July. That judgment, and the underwhelming BBB- rating it assigned to the bank, carries more weight now that new CBR rules that give more weight to credit ratings agencies’ judgments have now come into force.

Founder Vadim Belyaev, an old confidante of Boris Yeltsin’s discredited privatisation guru Anatoly Chubais in the 1990s, took back the reins as CEO at the start of August, but it’s not clear that he’s had any success in turning things round. If anything, the problem appears to be spreading: CBR data for the whole Russian banking sector, which are updated daily, show that the aggregate reliance on its emergency fixed-rate repo funding has risen to its highest in over a year (barring the usual year-end spike).

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Over the last few years, the CBR has been on a mission to close down as many under-capitalized banks as possible, in order to improve confidence in the system and prevent the kind of financial crisis that destroyed Yeltsin’s legitimacy in 1998. Governor Elvira Nabiullina has to tread a fine line, targeting ever-larger banks while trying to avoid triggering panic and depositor runs. The latest bout of volatility appears to go back to her decision to close Yugra Bank, the country’s 15th-largest, in July.

Nabiullina’s clampdown is taking place against the backdrop of an economy scarred by sanctions, a collapse in oil prices and a chronic corruption problem (neatly illustrated last year when a senior anti-corruption official was arrested with over $120 million in cash in his apartment). GDP contracted for seven straight quarters before rebounding gradually this year. At 2.5% in the year through the second quarter, it’s now growing at its fastest rate since 2012.

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But the recession has left a trail of bad loans across much of the economy, which many fear have not been fully acknowledged. Even according to Otrkytie’s accounts, some 7.5% of its loan book was 90 days overdue at the end of last year. ACRA’s estimate of non-performing loans in the system is much higher than the CBR’s.

Even after allowing for the effects of the recession, it wouldn’t be Russia (and it certainly wouldn’t be August in Russia), if someone weren’t vigorously stirring the pot.

Alfa Capital, an affiliate of one Alfa Bank, one of Otkrytie’s biggest rivals, said in a research note earlier this week that an increasing volume of “public and non-public information” had reached it suggesting that not only Otkrytie, but three other large Russian banks were in danger of collapsing by the end of September. Otkrytie called it “an information attack on the bank,” while Promsvyazbank called it an example of “bad-faith competition” – a designation that the antitrust regulator FAS appeared to agree with on Thursday. FAS deputy head Andrey Kashevarov told local news agency RIA. He said FAS will be issuing a formal warning to Alfa in the next few days.