I've just been testing by running "cat /dev/serial0". No reason to start gpsd if I can't see the NMEA sentences coming across the serial port!
I just downloaded Raspian 9 Stretch, with the 4.14.98 kernel and it works correctly.
Similar dmesg output:
ttyS0 at MMIO 0x0 (irq=166, base_baud=31250000) is a 16550
My conclusion is that something changed between Stretch and Buster.