WiFi icon PARTLY greyed out
I have two iMacs running WiFi from a Vodafone network. The two computers are next to each other. On one, I have a full black WiFi icon in the Finder toolbar. On the other, just two feet away, the icon sometimes is partly greyed out. Despite this, it appears to work satisfactorily. I've checked that both computers are connected to the correct Vodafone network - they are. I've tried turning the wiFi off and on again, removing and replacing the icon, restarting Finder and restarting the computer. None of these have solved the problem. Here's what the icon looks like:
It isn't desperate, but any ideas would be welcome.
Mac mini, macOS 10.14