I haven't experienced this problem, exactly, but I have had issues with noise in digital circuits that appear to have gone away with touch up.
The problem was that the customer blamed the noise issue on the solder quality, and he pointed to the fact that on touch up, the noise went away. It turned out, however, that there was a component problem, and when the IC was touched up, the heat of the iron caused the problem to go away. I don't know the final outcome, but it seemed that the heat of the iron on the IC body caused something internal to the IC which caused the circuit to work. The IC continued to function long enough to get through test. However, when the circuit cooled completely down, the units would stop working again.
So, I'm saying that you may not have a stray oscillation problem caused by solder voiding (not saying it's not possible, though); but that you may have deeper problems in your components.
cheers ..rob
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