Saying "Bonjour" more than once a day to the same person is not particularly polite!
Something new I learnt a little while back is that once you greet someone with "bonjour", you shouldn't repeat this greeting again to the same person during the day. It can be considered to be rude.
If you say "bonjour" again, it gives the impression that you haven't yet seen them that day, or that you don’t remember saying it before, or worse, took no notice when you greeted them earlier.
It's like saying "nice to meet you" to someone in the morning, and then you run into them again during the day and say again "nice to meet you".
So if you say "bonjour" again, the person may look at you in a funny way and say something like: “on s’est déjà salués” (we already greeted each other).
Instead of saying bonjour several times, the second greeting can be something along the lines of "re-bonjour!" or something nice like:
"ça va depuis tout à l’heure"? (all good since earlier?).
Or just "ça va"?
I go for the latter as it avoids the difficult french "r" sound in "re-bonjour"!!
or just a simple acknowledgement, smile and wave.....