Fresco eraser brush stop working.

Hi friends, suddenly several of the eraser brushes stopped working for me. Some are still fine, but several of them just don’t work at all — and this only happens on pixel layers. For example, the issue occurs with the basic Eraser brush, as well as with “Opacity of Circular Defined” and “Opacity of Circular Diffuse”. I’ve checked the settings, closed Fresco, deleted it from the iPad, reinstalled it — I’ve tried everything. Does anyone have any idea what might be going on? Thanks a lot.