I believe I have found a bug with the filtering function. I have two different pages on my web site with two different occurences of the Daypilot scheduler, and the filtering is working nicely on of them them but not on the other and I have spotted the difference between them.
So, I have an input field where you write your filtering string and for each character written here, the onEventFilter() is called and the filtering is done based on a "searchtext"-property set in the different events. This works UNLESS you have implemented the onBeforeEventRender(). It doesn't even matter if there are any code in it, as soon as you have the onBeforeEventRender() in your config of the calendar the filtering doesn't work as expected.
In this case, the filtering is delayed for one character. So if I start to write the character 'a', no filtering is done. Then I continue to write 'b' so the filtering string now is 'ab', but now the filtering is done just for 'a'. And so it continues, if write 'abc' it will filter on 'ab', and so on.