3 FPS on heavy content

Hello,

in normal operation game run at around 55-60 FPS
GPU 99% usage, CPU 15%

But sometime, on some maps, graphics freezes, goes to 3FPS,.
to remove this condition, I have to exit to character selection, and come back.
But once a maps starts doing that, I may have to do it 10 times per map.

During theses freezes CPU is a 15% and GPU at 35%
Graphics of monster fighting are stuck, but menus are responsive, like esc to exit to charater selection, or menu, or inventory

Last map with issue was augury with delirium, abyss, Boss and corrupted