Seems to be a common issue with Galaxy's and maybe other Samsung Android phones.
Whilst playing about, I noticed that the signal strength reading is available in the Settings / About device / status area. I later noticed that a signal strength widget was now working.
'Strange', said I to myself- never had a signal strength widget work on this phone before!
At first I thought it was that a new widget I had recently downloaded had somehow been written in a different way, that works on Galaxy phones, but a few checks later and I noticed all the signal strength tools I had previously downloaded were now giving proper readings.
A few more checks and it seems that providing you go to the "Settings / About device / status area" after and re-boot, your widgets will work. You don't have to click on anything on the page, just open it!!
Thought I'd share this discovery with anyone interested.
Oh, and by the way, a good signal strength widget - my favourite one is https://play.google.com/store/apps/details?id=de.android.telnet2. This widget has several sizes, and if you tap it it shows lots of details. In the detail you can tap the bar signal strength indication to get an analogue meter of signal strength. Also gives WiFi readings and there is a free version with ads you can use first to test it all works - especially those of you with Samsung Galaxys!
Anyway - thought some of you might find this discovery of interest.