Who I have the same questioned this topic

Over the last 4-5 weeks the signal strength for our phones has declined.  We have phones from LG, Samsung, and Apple and all are getting poor LTE signal and frequently now switches to 3G which also has poor signal.

Checking things right now on my S6, the LTE signal strength is -115 with SNR of 138.  There is little difference inside my home versus outside.  The zip code for the area is 28348.  While I do not have signal strength readings prior when the coverage was better, the signal strength indicator on the phone was always at the 50% range (3 bars) while now it frequently indicates 1 bar or less.