At a first look, they seem too close to each other. In general, capsules with a radiator tab rely on the PCB copper for heat dissipation. Use an infrared camera to measure the temperature of each chip during the worst working regime, inside its enclosure and at the highest expected room temperature.
Apart from that, I would also look for very high frequency oscillations, or if the absolute maximums request of the datasheet are obeyed at all time, including during transient regimes. Even when the schematic is correct, a bad layout of the PCB traces might make a stable circuit unstable.
It's hard to identify the reason without schematic + PCB layout + mechanical enclosure.