FWIW, removing libglvnd0 fixed the problem (libegl1 does depend on it, but it isn't installed in artful either - libegl1-mesa is).
So the bug is actually:
a) the upgrade from artful to bionic installed libglvnd0 and libegl1 when they aren't needed;
b) having libglvnd0/libegl1 installed breaks EGL on Intel-graphics systems.
FWIW, removing libglvnd0 fixed the problem (libegl1 does depend on it, but it isn't installed in artful either - libegl1-mesa is).
So the bug is actually:
a) the upgrade from artful to bionic installed libglvnd0 and libegl1 when they aren't needed;
b) having libglvnd0/libegl1 installed breaks EGL on Intel-graphics systems.