Why does my Maps app on Mojave no longer show the correct highway shields?

I'm wondering if it's just my computer - I've even reset to factory settings and re-installed Mojave, but my Apple Maps no longer shows the correct highway signs. I live in England now, so it's less of a big deal [although some signs should be blue, some green, and some white], but look at my hometown of Minneapolis, USA:

169 should have a US Highway shield, 494 should have an Interstate Highway shield, 100 and 5 should have a Minnesota highway shield, other roads like 21, 31, 32, 53 - should all have county road shields.

This used to be fine on my MacBook, and everything is still correct on my iPhone and iPad.

I don't want to upgrade to the next MacOS (Catalina) as 1 - I no longer would be able to open some 'antique' apps (32 bit app support was dropped) and 2 - my old MacBook may go extremely slow with Catalina. (I don't think I can upgrade beyond that on my 'vintage machine').

Anyone else on Mojave notice this strangeness with the highway signs?