While playing on the latest experimental build (0.62.139977), I noticed that the main menu would freeze up for a very short duration both when I pressed as well as released the primary mouse button, regardless of wether I was clicking on a button in the menu or not.
Furthermore, the buttons in the menu were sometimes very unresponsive. It took me 5 mouse clicks to activate a button in the menu one time. This varied though, and other times it took me only one or two to three mouse clicks to activate a button.

I only experienced the main menu stuttering and mouse buttons being unresponsive on the 64 bit client, thus this issue maybe be related to: https://feedback.bistudio.com/T125606 .