Entire message history deleting after trying to delete messages individually

[Faztcobra]

This has started after the update to Nougat. I will highlight messages one by one to delete single messages I no longer want to keep. Then I hit delete - then it deletes EVERYTHING from that text thread. Sometimes it does it, sometimes not, but I would say greater than 50% of the time. Messages I've saved for weeks or months - poof into thin air. Never had a problem before in 2+ years with my 6. Any thoughts on how to correct this?