I have got the following graph:
Here you can see a graph of a device which is turned on and turned off a short time afterwards. as you can see, there are very short "high" periods. On the 7th Period, the points are so close together that AmCharts just merges them into one. If i zoom in just a little bit more, it will look like this (which is how it should look):
I did not yet manage to find a property to configure this behaviour.
I found out the the reason for this behaviour is this line:
am4core.options.minPolylineStep = 5
which I now removed and fixed my problem! It would be interesting to know if this property can be configured independently for series (it does increase performance, so using it for lineSeries is a good idea)