That does seem counterintuitive, we will take a look on our side and see if we can reproduce that issue.
In terms of general limits, we have seen that performance of larger dashboards can vary wildly between different computers and browsers. With the map in particular, we have seen that the drawing of the path lines between data points can be surprisingly costly. We are actually doing a general “dashboard performance” pass at the moment, which will hopefully address some of this.
The pagination of devices on a map is a neat idea, we will toss that around internally, see how that would feel on that dashboard block!