OK I accept some of what you say except I have GPSD running under Ubuntu Mate 16.04 and Indiserver indi_gpsd both locally and remotely without changes to the std GPSD file(s). This is with the Ublox7 USB dongle.
Not criticism's
just trying to get to the bottom of the Users problem which should work "out of the box" and learning
On my std Ubuntu Mate 16.04 i find this Points
1. There is no device hard coded into my GPSD default file as I assume with the UBLOX7 the "AUTOUSB" default option, allows for the UBLOX7 to be started at boot or "hotplugged" and the device added. My working file without Ublox7 inserted looks like
# Default settings for the gpsd init script and the hotplug wrapper.
# Start the gpsd daemon automatically at boot time
START_DAEMON="true"
# Use USB hotplugging to add new USB devices automatically to the daemon
USBAUTO="true"
# Devices gpsd should collect to at boot time.
# They need to be read/writeable, either by user gpsd or the group dialout.
DEVICES=""
# Other options you want to pass to gpsd
GPSD_OPTIONS=""
2. The UBLOX7 ,when plugged in,actually defines itself as a ACM device and uses ttyACM0 on my Ubuntu Mate 16 - I have never looked for any udev rules/Daemon etc if they exist. as the Man pages say
"The serial device may be specified to gpsd at startup, or it may be set via a command shipped down a
local control socket (e.g. by a USB hotplug script). Given a GPS device by either means,
gpsd discovers the correct port speed and protocol for it."
So my question is in this case,a UBLOX7, will the hard coded serial not cause a problem ?
3. I do not have any of the PPS/GPSD lines reported into my logs (even if the UBlox7 is not plugged in) but except your reasoning for the difference.
4. I have found that GPSD has a nasty issue with leaving "old" Unix/Linux symbolic links which can cause problems if you use different GPS devices or configurations. Best removed by removing GPSD and Clients then reinstalling.
6. In the end the user has got to provide more real info from logs for anyone to sort his/her problem
I based my finding partly on this thread (ok its for Stretch)
www.raspberrypi.org/forums/viewtopic.php?t=56023
Oh I forgot to say "Happy New Year" (including many clear skies) to you and everyone else