Points are really calculated on the server side. The client is side is purely approximate, and may give you points in places where you might not be eligible. So corrections and delays in processing might cause up and down swings.
IE: I've had roads that I've driven on in the past, show up with dots again. The client gives me the points because of the dots, but the server when it calculates my true points, may not give me the points because it remembers I have driven that road already.
IE #2: Or the client thought I was on one road but when analyzed by the server which use a more exact algorithm it shows I was on a road that I already got points for.
I won't admit there are scenarios which cause points to be lost. Most of them seem to be related to connection issues, and the client not connected back to the servers correctly. The devs are actively working this (I know, I've been sending them logs, and chatting to them about it).
The other issue is popularity. The product is in start up mode. A good thing, they have gained a lot of popularity. The bad thing, the servers are having a problem keeping up. The points are suppose to be calculated daily, but the amount of data coming in, is making it so that process is falling behind.
Also note that Rank is not directly related to point total. There are a lot of people running the application so even if you run a lot points up, so could everybody else.
The whole points/rank thing is being reworked behind the scenes, so for the time being. Just go with the flow. The goal here is to make the best maps/traffic/social network.