It's a Cat B15Q, with Android 4.4.2, with most recent update as issued by Cat. I think it started with the most recent update. Unfortunately, Cat's support site doesn't work (you can't submit questions), so maybe someone here knows.
The phone always has a decent connection to WiFi, according to the icon. But after a while (it can be an hour or just 5 minutes), it no longer connects to the internet. I observed this on three different WiFi networks. Disabling and enabling WiFi fixes the connection, for a while. I disabled all sleep and battery saving options, but to no avail. It's driving me mad!