I cannot prove it but it may be due to carriers implementing various tools to prevent the scam calls. My carrier is VZW and recently they pushed out their Call Filter app to try to intercept such calls. I did download the update and have noticed an uptick in the number of times I see a call was received (in notifications) but phone never rang nor beeped.
Since this is something that I have no control over, I just call back the contact who called me; hoping that call connects. Alas, it is the ever escalating battle between the carriers and the scammer/spammer contingent.
BTW, I never buy extended car warranty, even on a new car purchase.