UI drawn correctly on startup but garbled on update

For instance, lv_example_get_started_4(); draws a slider correctly but it becomes garbled on update. Video here: https://www.youtube.com/watch?v=LU9YAgiciBw

I use LV_USE_GENERIC_MIPI so the flush function is the unmodified flush_cb from lv_lcd_generic_mipi.c.
To create the display, I use: lv_lcd_generic_mipi_create

Of course, in simulator everything works as it should.

Appreciate any ideas…