Garbled Text in Kubuntu Launcher Menus (20.04)

I successfully (mostly) system-updated my 18.04 Kubuntu system to 20.04 for the first time after multiple attempts with the last several LTS versions. I say "mostly" because as my system runs, the Launcher menu and submenus gradually deteriorate and become unclickable. I have a jpeg of what this looks like but there doesn't seem to be an option to attach that to this post.

I have a theory that the text characters are not actually disintegrating, but are being overlapped by other menus(?) or something. These overlapping things are also preventing me from clicking on the underlying menu items. When first booted, the Launcher menus are "normal"

This machine is a VirtualBox guest of a Windows 10 host. System Info:

Kubuntu 20.04
KDE Plasma Version: 5.18.5
KDE Frameworks: 5.68.0
Qt Version: 5.12.8
Kernel Version: 5.4.0.91-generic
OS Type: 64-bit
Processor: 1 x Intel Core i5-4690K CPU @ 3.5GHz (Host has 4 cores)
Memory: 7.8 GiB of RAM (Host has 32GB)

I typically run 8 desktops, 4 of which have terminals. Beyond that I run Calibre, KCalendar, Firefox and Dolphin. System Monitor shows typical resource load around 20 - 50%.

Anyone have any thoughts about this issue?