I have a Samsung Galaxy Tab S2 (tablet from 2015ish) and a Samsung Galaxy S8 and neither one can see 1 specific WiFi network. My girlfriend's older Apple cellphone can see it. Both of my devices can see all of the other nearby WiFi networks, just not the one I should have access to.
I have tried restarting both the router as well as my two devices. Also had a guy come by with a Nokia cellphone running Android who was also able to see the network.
Thoughts? Suggestions? I am at an Airbnb, so it isn't like I will be here long, but it would be nice to not have to tether to my girlfriend's cellphone.
NOTE: If none of the following work to resolve the problem, and if the tablet is under warranty, I would contact the manufacturer.
1. Try and restart the tablet. Sometimes it is that simple.
2. Update the firmware and any apps that need updating on the tablet.
3. If the problem persists, check your time and date on the tablet to make sure it is correct.
4. Should none of the former work...
a. Clear out the WiFi data on the tablet.
b. Reboot the modem/router.
c. Once the modem/router is fully 'up' again, reboot the tablet and re-input the WiFi data.
5. Check your internet connection. It may be what is going in and out rather than the tablet.
6. Make sure you have "Data" turned off on the device when using "WiFi" (that is if you have a plan with data through your tablet). If you don't make sure it is turned off, the device can keep trying to switch to "Data" when you try and use "WiFi".
7. It actually may be the type of WiFi they are broadcasting on and not your device.
There are two kinds. 2.4GHz and 5.0GHz. Older devices tend to only access 2.4GHz ones where as many newer devices can access either, at least of they are both turned on within the device.
You need to check and see which one your device uses/needs and which one the other devices are connecting on. You should be able to find the info in the devices that can connect. For a phone or tablet that is connecting, go into "Settings" and then "WiFi". Locate the network they are connected to and tap it to open the info. You should see a listing for "Frequency" which will tell you which it is, 2.4GHz or 5.0GHz. Then you need to see if your tablet needs a different network.
8. Now, if you are still having the problem at this point, and you are sure it isn't the modem/router that is the problem. Then you may wish to try a "Hard Reset" of the device. However, I really suggest saving this as a last option (or last before parts repair/replacement).
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually powered off.
2. Press the "Power" and the "Volume Up" buttons, together, until you see the start-up logo on the screen.
3. Once you can see the logo, release the buttons and allow the device to enter the "System Recovery Mode".
4. Next use "Volume Down" button to get to the "wipe data/factory reset" option When in recovery mode the "Volume Up" and "Volume Down" buttons are how to can navigate and highlight what option you need.
5. Once you have selected the "wipe data/factory reset", press the "Power" button to select that option.
6. On the following screen, repeatedly press the "Volume Down" button until the "Yes - delete all user data" option is what is selected.
7. Then press the "Power" button to hard reset the tablet.
I included all options I could think of, hence the reset.
If only your device(s) can't see it, and you have both options available on your device(s), and said device(s) work on other WiFi, then the issue would be with that WiFi.
While you said you restarted the modem/router, this would not effect anything done in the modem/router setup. The only options left I can think of is restrictions in there. That, however, you would have to get the owner of the network to look into. It could be the number of devices allowed, any type of device it may have restricted, etc. Those settings can only be accessed by logging into the modem/router settings.