The monitor should not go in the filter or skimmer. It needs to float (although you can take it out for a few hours while people are swimming).
There are a few reasons for this:
First, the monitor isn't able to communicate with the wifi bridge when it's in the skimmer. The other reason is because the skimmer contains leaves and other debris that deteriorate over time, and that can throw off your readings. Especially if they, and the monitor are in a small confined space.
This is especially true for all those hours when pump is not running, and the water in the skimmer stagnates a bit.