A grey GPS icon usually means the GPS sensor hasn't locked onto enough satellites to give you an accurate position.
As one person said earlier, download an GPS app that can give you detailed information on the satellites that the device can see, their signal strength etc. The app will rule out the possibility that there is a hardware problem (ie. no satellites are in view even though you are outside and in full view of a clear blue sky).
Another person said they get a white GPS icon in 5 seconds. I do too. How it does this is more complicated behind the scenes. Pure GPS devices don't normally lock onto satellites within 5 seconds. This is because on startup, the GPS chip has no idea what satellites are in view, nor do they know what satellites should be seen. So it has to pick up the satellite signals, then get enough data to triangulate your position. Some will say this is not true... that their GPS locks on within seconds. This is probably because the GPS is fed prexisting data that is either hardcoded or cached for quicker lockons. As for our smartphones, what used to happen (as I'm not sure if modern smartphones still do this) is that it will get a rough location based on cell towers, then go out to the Internet and obtain the data so that the GPS doesn't have to acquire it on it's own... then it caches this data so the next time it won't have to go to the Internet as often. This is called Assisted GPS.
As for your situation, it could be that the installation of the update has wiped the cache or some internal settings from the device. My advice is to download the GPS app and go outside on a clear day and wait for the app to get a GPS lock. I could take minutes, but the benefit of the GPS app is that you are not just looking at a grey icon, but you're able to see what it's actually doing. If it locks, then there is nothing wrong with the GPS hardware itself, but probably something wrong with software and maybe the update hosed something.
I used to load a lot of custom roms on previous phones I owned and I ran into GPS problems as well. This was years ago so my memory is a bit faded on this, but the ROM maker changed the a-gps server to suit his own location. Well, since I'm in a different part of the world, the a-gps server probably didn't have the correct satellite information for my location, so GPS locks would take a long time because the "Assisted" part didn't work. It was only after I changed the a-gps server to one that serviced my continent that gps locked on faster. I don't know if modern smartphones still use a-gps servers or solely obtain the information from cell towers.
Now, I don't know how similar your G5 is to my G3, but when I enter the service menu on my G3 (google G5 service menu to see the code you need to enter on your phone dialer), I have a GPS option in the menu. In there, I'm able to perform a GNSS test, GNSS pos test, and air test. In the GNSS test, it actually has a GUI that shows the satellites it can see and it's state of lock. See screenshot here:
If you can get into the service menu and find the GPS option, maybe perform this test to prime the GPS device as it appears to cache is at the OS level or below (the menu at the top right 3 vertical dots has an option to delete "aiding data". The service menu can fix a lot of things, but you must be careful with what you do.
Oh, I forgot to mention to go to your Location settings and make sure high accuracy is enabled (you probably do but I want to make sure to cover the bases).
