Reviving this topic a bit; may I ask what your sample size was? I've experienced 5 bold syncs in 45 catches, and 22 failed syncs in a row. This is with the ability still listed as 'synchronize' in the stat panel after fleeing an encounter, but listed differently from the stat panel via linked pokemon in chat.
I don't have a background in statistics, so this might be an example of gambler's fallacy or whatever. However, the likelihood of getting 22 failed syncs in a row is close to a 1/4 000 000 chance. I realize that this is still a relatively small sample size, but I'm reluctant to do further testing when it may be a waste of my time. Well, if this can be simply described as bad luck, it would remove the necessity of relogging after every single encounter.