Very high CPU usage under GNOME 3.32

Enabling the extension on GNOME 3.32 (Archlinux) raises gnome-shell CPU usage to ~70% on one core, while without the extension enabled it's between 0 and 15%.

It will sound very weird, but it seems like opening the extension settings window from tweak tools has a serious impact on the CPU usage: opening it once will lower the usage down to ~0%, and opening it a second time will raise the usage to ~70%, the third time will lower to ~0%, etc. that's crazy...