I had this happening to a few random contacts and it was frustrating. The one thing in common with the contacts for whom my phone would not save text message history is when I viewed their Contact profile there was a What'sapp version of the contact. This is an option like Google, Phone, Samsung, etc. I am sure I could have figured out how to delete the what'sapp version of the contact, but I just deleted whstsapp and it solved my issue. I never contacted these particular contacts via what'sapp. I can't really explain how their what'sapp profile became part of my contacts. But after months of being frustrated by this, I cautiously optimistic I've resolved it.
I had only one conversation disappear. I don't remember deleting it, as I rarely do! I have a Samsung Galaxy LUNA pro. Also-- on my info for the device says it's a different model: Galaxy j3 pop (i think)
Should I be alarmed?
How do I change this ? Or is it one in the same??