On the B737 NGs there were a number of incidents whereby the hydraulic pumps used to fail one after another when the temperature at altitude was significantly below ISA. On one occasion,three of the four hydraulic pumps clocked out (both electric and one of the two engine driven) before a descent to warmer air fixed the problem. I understand that a modification of the hydraulic plumbing has largely fixed this problem, although the odd single pump failure isn't unheard of.
Also on the same subject (temperatures below ISA) it wasn't uncommon for the A340s to have to descend to lower (warmer) levels because the fuel temperatures were getting dangerously close to the freeze point. This was particularly common on the northern siberian routes (to Hong Kong / Tokyo) during the middle of winter. Airbus in their wisdom had decided that fuel heaters weren't necessary, but line experience proved them wrong. Transferring fuel around from tank to tank, flying faster, or as a last resort, descending, were all well tried "tricks" to fix the fuel freeze problem.
I suppose the day which prompted the original question had temperature conditions low enough to cause hydraulic problems for some aircraft types and fuel temperature problems for others?