Sony reported another quarter of record profit, but weakness is bubbling just below the surface.

The 72-year-old Japanese electronics and entertainment giant said Friday its operating profit had risen 7% to 377 billion yen ($3.5 billion) the previous quarter. Almost a third of that came from a one-off valuation gain from its $2.3 billion acquisition of a 60% stake in music publisher EMI in November. Stripping that out, Sony’s operating profit actually fell 26%.

The...