For the record here...

Jasem found the problem.

This file was missing:
/lib/udev/rules.d/60-gpsd.rules

Recreating the file with this in it fixed the problem:
SUBSYSTEM=="tty", ATTRS{idVendor}=="1546", MODE="0666", SYMLINK+="gps", TAG+="systemd", ENV{SYSTEMD_WANTS}="gpsdctl@%k.service"

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