When a non-Eurozone central bank holds euros, it tends to deposit those euros with the ECB. So when the Fed executed its liquidity swap, it received euros as collateral and deposited them in its account at the ECB. That deposit by the Fed created a "non-Eurozone resident" liability at the ECB.
But the Fed's liquidity swap is now a fraction of what it was at its peak. The ECB returned the dollars and the Fed returned the euros.
|Fed Liquidity Swap|
That means the ECB's liability to non-Eurozone residents should have declined. And it has, until recently. But now we have a new spike in non-resident liability at the ECB. So who outside the Eurozone is depositing a massive amount of euros? The Swiss National Bank (SNB) of course. As as the SNB defends the Swiss Franc from strengthening (trying to keep the peg at 1.2), it buys a great deal of euros and of course promptly deposits them at the ECB, increasing the non-resident liability .
Therefore this second spike is created by flight of capital our of the Eurozone (the ECB provides this data on a weekly basis allowing one to monitor the trend closely - ht Kostas Kalevras). Note, these euros are still held within the Eurozone (the amount of euros is always fixed unless the ECB chooses to change it), but they no longer belong to Eurozone residents. These Eurozone residents have swapped their euros for Swiss Francs.
ECB balance sheet