When working with log data or any other form of data with text, I use the list box filter a lot. I can scroll through the list to view the available values based on other filters. I frequently use search to look for a particular word or phrase among longer text values in a list box filter. But there is no easy way to select all the search hits. I have to click the first value, then scroll down to the bottom of the list, hold Shift and click the last value. I then typically scroll back up again so I can see the (All) number to get a feel for how many values I've selected compared to the available. Just as with any search I typically iterate a lot to try different variations of search phrases which makes this workflow feel cumbersome.
I suggest to add another option right below (All) when a search has been performed, which would similarly show the number of hits so I can compare with the All value, and then with a single click select all those values.