Sometimes launcher right-click menu of, for instance, Files gets stuck on screen and eventually causes Gnome UI to become totally unresponsive.
When I right-click and don't select a menu item and click elsewhere, right-click menu gets stuck on screen, and overlays any other active window. Or else I select a menu item of it, then whole screen items become unresponsive except cursor. After that, when I lock and unlock the current user session, then stuck menu disappears and screen becomes responsive.
I encounter this problem more frequent than occasionally.
Dell Inspiron 3543 Ubuntu 18.04 LTS Memory: 7.7 GiB Processor: Intel® Core™ i7-5500U CPU @ 2.40GHz × 4 Graphics: GeForce 840M/PCIe/SSE2 Gnome: 3.28.2 OS type: 64-bit
sudo lshw -c video *-display description: 3D controller product: GM108M [GeForce 840M] vendor: NVIDIA Corporation physical id: 0 bus info: pci@0000:08:00.0 version: a2 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list rom configuration: driver=nvidia latency=0 resources: irq:52 memory:f6000000-f6ffffff memory:e0000000-efffffff memory:f0000000-f1ffffff ioport:d000(size=128) memory:f7000000-f707ffff