Tipping neighbors I've already tipped

I hope that I have posted this in the correct location. I am having this issue in both RS and BS. I am running on Android v2.3.6 and RS v1.5.5.2 and BS v1.5.5.2.

I usually go through and tip my neighbors early in the day. Sometimes, I will return to their restaurant after they have visited me and realize that I have tips left to give them. I already gave them max tips and I have already posted that on their wall. Why aren't all the tips being counted? I don't want my neighbors to think that I'm lying! This happens randomly and it's not the same neighbor either. I would say this happens several times a week in both games. Does anyone have any answers?

Maybe you are tipping some of them just before the game "resets" (12 AM PST) and when you got back to their bakeries and restaurants post-reset, you are able to tip again.

If someone else tipped the same table and it got to the server before your tip, your tip won't count.

If the server is slow, or your internet connection hangs or is slow, sometimes the tips won't get to the server and won't count.

Thank you both for your replies. I am going to assume that it is someone else tipping at the same time as I am. 12 AM PST is 2 AM where I live and I can guarantee that I am fast asleep! :D