Of course, the day after I post this report, an update appears to have fixed the bug.  I can't really tell which package was responsible.  Here's the list

Install: libwayland-egl1:amd64 (1.16.0-1ubuntu1~oibaf~b,)
 gnome-software:amd64 (3.28.1-0ubuntu4.18.04.4, 3.28.1-0ubuntu4.18.04.5,)
 gnome-software-common:amd64 (3.28.1-0ubuntu4.18.04.4, 3.28.1-0ubuntu4.18.04.5,)
 gnome-software-plugin-snap:amd64 (3.28.1-0ubuntu4.18.04.4, 3.28.1-0ubuntu4.18.04.5,)
 kmod:amd64 (24-1ubuntu3, 24-1ubuntu3.1,)
 libdrm2:amd64 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm2:i386 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm-amdgpu1:amd64 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm-amdgpu1:i386 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm-common:amd64 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b)
 libdrm-intel1:amd64 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm-intel1:i386 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm-nouveau2:amd64 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm-nouveau2:i386 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm-radeon1:amd64 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libdrm-radeon1:i386 (2.4.96+git1810220630.9d07fb~oibaf~b, 2.4.96+git1811020630.b3dec0~oibaf~b,)
 libegl1-mesa:amd64 (18.3~git1810241930.edc06d~oibaf~b, 18.3~git1811011930.1f4110~oibaf~b,)
 libegl-mesa0:amd64 (18.3~git1810241930.edc06d~oibaf~b, 18.3~git1811011930.1f4110~oibaf~b,)
 libgbm1:amd64 (18.3~git1810241930.edc06d~oibaf~b, 18.3~git1811011930.1f4110~oibaf~b,)
 libgl1-mesa-glx:amd64 (18.3~git1810241930.edc06d~oibaf~b, 18.3~git1811011930.1f4110~oibaf~b,)
 libkmod2:amd64 (24-1ubuntu3, 24-1ubuntu3.1,)
 libpython3-stdlib:amd64 (3.6.5-3ubuntu1, 3.6.7-1~18.04,)
 libwayland-egl1-mesa:amd64 (18.0.5-0ubuntu0~18.04.1, 18.3~git1811011930.1f4110~oibaf~b,)
 libxatracker2:amd64 (18.3~git1810241930.edc06d~oibaf~b, 18.3~git1811011930.1f4110~oibaf~b,)
 linux-generic:amd64 (4.15.0.37.39, 4.15.0.39.41,)
 linux-headers-4.15.0-39:amd64 (4.15.0-39.42, automatic,)
 linux-headers-4.15.0-39-generic:amd64 (4.15.0-39.42, automatic,)
 linux-image-4.15.0-39-generic:amd64 (4.15.0-39.42, automatic)
 linux-image-generic:amd64 (4.15.0.37.39, 4.15.0.39.41,)
 linux-modules-4.15.0-39-generic:amd64 (4.15.0-39.42, automatic,)
 linux-modules-extra-4.15.0-39-generic:amd64 (4.15.0-39.42, automatic,)
 mesa-va-drivers:amd64 (18.3~git1810241930.edc06d~oibaf~b, 18.3~git1811011930.1f4110~oibaf~b,)
 mesa-vdpau-drivers:amd64 (18.3~git1810241930.edc06d~oibaf~b, 18.3~git1811011930.1f4110~oibaf~b,)
 python3:amd64 (3.6.5-3ubuntu1, 3.6.7-1~18.04,)
 python3-gdbm:amd64 (3.6.5-3, 3.6.7-1~18.04,)
 python3-minimal:amd64 (3.6.5-3ubuntu1, 3.6.7-1~18.04,)
 xkb-data:amd64 (2.23.1-1ubuntu1, 2.23.1-1ubuntu1.18.04.1,)
 xserver-xorg-video-amdgpu:amd64 (18.1.99+git1810241933.c9d43c~oibaf~b, 18.1.99+git1810291933.1cb338~oibaf~b,)
Upgrade: libcurl3-gnutls:amd64 (7.58.0-2ubuntu3.3, 7.58.0-2ubuntu3.5)
Upgrade: libcurl4:amd64 (7.58.0-2ubuntu3.3, 7.58.0-2ubuntu3.5)
Upgrade: linux-headers-generic:amd64 (4.15.0.37.39, 4.15.0.39.41,)

SOLVED for me.