Two big loans that were made during the postpandemic boom in private-equity buyouts are defaulting, whacking some private-credit funds and ratcheting up losses in the already troubled corner of Wall Street.

Software maker Medallia—a poster child for the intersection of investor concerns between technology and private capital—can no longer repay about $3 billion of loans from firms including Blackstone BX -2.03%decrease; red down pointing triangle, KKR KKR -1.90%decrease; red down pointing triangle and Apollo Global Management.