What were you doing before bug occurred: Opening my inventory while a filter was already active before.
Steps to reproduce: When you have a lot of items, use any filter, then while the filter is active, close and re-open your inventory (can be done with any window that uses a list of items, not just your inventory). This framerate drop only happens AFTER the filter was already in use before you opened a list of items.
F9 Logs ( press f9 to view them in-game): It was blank. I checked before and after repeating the bug. However the GPU bar graph appears to get maxed out when this bug occurs.