Believe me PWT999, I would tell you if I knew as it was driving me nuts as well!!! I had also put in a Support Ticket but had only received the acknowledgement in return. I assumed when the problem seemed to clear, that they had done something at their end. I had previously like you tried various settings and unpinned the popup etc. The current situation is that I only have a "slight issue" now on Desktop A---my main PC. I have Desktop A (Win10Pro), LaptopB (Win10Home), Desktop C (Win10 Pro) and Desktop D (Win10 Home). All are at the same version--1809 Build 17763.194. I only run Windows Defender, Malwarebytes Premium and CCleaner Pro.
Desktop A this morning at power up displayed the popup and I didn't touch anything. It slowly faded before finally disappearing after about 10 seconds. Firing up CCleaner did not bring it back. Neither did a power down and a power up. Don't know if that'll happen tomorrow but will be going out shortly so will try powering it up later. Not much time at the moment. Took snapshots of what settings I have and also what cookies I keep. I remember removing the Avast one previously --but that was before I realised Piriform had been taken over. It is on two of them. Attaching snapshots in a zip file. Hope you can access it--if not I'll post them individually.
Screenshots.zip