It sounds like to me a faulty solder joint (crack between the smd pin and the pad). Cooling probably causes a differential contraction which brings the pin into better contact, and of course clamping achieves the same.
It may have started with a hairline defect that got worsened by thermal cycles.
If it is a bad solder joint, reflowing bridges and fixes the joint. It won't harm the chips as long as the temperature is correct, since it needed to be soldered in a reflow oven in the first place. However (I believe) there is some risk of excess heat corrupting some data, and/or worsening the defect, so if you can back up first using the jury-rig, that's certainly preferable.
It may have started with a hairline defect that got worsened by thermal cycles.
If it is a bad solder joint, reflowing bridges and fixes the joint. It won't harm the chips as long as the temperature is correct, since it needed to be soldered in a reflow oven in the first place. However (I believe) there is some risk of excess heat corrupting some data, and/or worsening the defect, so if you can back up first using the jury-rig, that's certainly preferable.