Poro King massive slowdowns in selection

I don't know why, but when I go into champion select for the poro king I get very bad lag. Waiting for the selection screen to appear after I have pressed "accept" takes about 20 seconds - so by the time I get into the lobby I only have 40 or so seconds to make adjustments. If I click on any of the screen options, such as rune page or re-roll, it basically freezes and then updates a few seconds later.

I do not get this issue with any other selection screen in the other game modes - it is specific to the poro king.