Went through them with tweezers to make sure they don't move but there you go.My technique was tinning the pads with flux (and solder) and then soldering the connectors with the heat gun. Had to touch up a few with the iron because they were moving.
Next time I'd use solder paste and heat gun.
Glad you found it.
Actually a customer of mine told me yesterday they had the same problem (they had soldered themselves). In the past we've seen this culprit often. Will see if I can improve the experience at a reasonable price.