I have observed that when I have a lot of nets / coppers / copper fill blockers / ... in the same area, it becomes more and more difficult to select the desired element.
Using the feature to hide unwanted layers does not help much.
I think that hidden layers are ... hidden! and not really removed, so to select a net for example, I have to click on this net and hope that there is not an element on an other (hidden) layer. Otherwise, it won't be selected.
This can become complicated when the number of nets / coppers / ... is important.
So, I would appreciate that the function that hide layers, make them hidden for the selection tool too.
Furthermore, it may be a different problem, but I think that it is linked to the previous item:
I have observed that it is possible to move a Copper Fill Blocker, which is on Top, whereas Copper Top Layer is hidden.
To reproduce this:
1- Start a new project, and open PCB view.
2- Make PCB 'Blocked' (otherwise, it may move during manipulations).
3- Place a Copper Fill Blocker on the center of the PCB, on Top layer.
4- Hide Copper Top Layer (menu View).
5- Try to move the Copper Fill Blocker (you have to remember where you had placed it). You won't see it, but if you click on it and move the mouse, it will move!
6- Display Copper Top Layer (menu View), and if you have clicked on the right position, the Copper Fill Blocker will be at an other position than initial.
I don't know if it is specific to Copper Fill Blocker, but for the moment I have observed this problem only with this element.