Have great signal but miss calls

[Snn5]

I believe this to be more of a network issue rather than a phone issue, however:

LG G2 VS980

Android 5.0.2

VS98039A

My data and voice signal are great, usually around 3-4 bars inside.

I can place my phone on my desk, make a call, and hold that call as long as I need without disconnecting.

However, I miss almost a 3rd of calls (that I know of) with the phone in the exact same spot.

Example:  I made a call last evening.  Call lasted over an hour.  That caller called me back 10 minutes later, but the call went straight to voicemail.

This happens often, though sporadic no matter if I was just on the phone with them or not.  This happens across 2-3 different carriers.  It seems the network does not know my phone is on and communicating with the network seeing as how calls go straight to voicemail.  Seems to me that, if the network was communicating with my phone, that the phone would at least ring for the caller before going to voicemail.  Obviously, my phone does not ring on my end.  I see no missed call in the log, nor do I receive any other notification.  I only know that someone called me if they leave a message, which will give me a notification, or if they actually tell me, "I called you, but it went straight to voicemail."

The phone has been replaced about 4 times, the SIM about 4 times as well.

I understand that service inside is not guaranteed, nor in all areas outside.  I have placed calls for network tickets many times.  I think most of us know how that turns out and what is involved.  So, I have tried the customer service angle before, but I think I need a more rational answer from real people who really know what might be happening.

My issue is my lack of understanding how a phone with great signal can miss so many calls.

Any ideas?

[Snn5]

I failed to mention that call forwarding is NOT turned on.