Maybe there's some malware onboard that needs extra tools to tackle.
Try running Malwarebytes Free, linked in the last line of my signature below.
There are other tools there that you can also try. (See Free 3rd Party Tools).
Thought of using Malwarebytes Free for this problem, but I did not want to mess up my McAfee installation.
Seems my mother-in-law virus checker trial period ended (like many years ago) and her laptop got infected with Windows Ultimate Booster. I used Malwarebytes Free to clean that up and then installed McAfee Internet Security on her laptop. (Took forever for McAfee to do a full scan. Stuck on "rootkit" for the longest time. But that is another problem.) Anyway, when I installed McAfee on her laptop, McAfee insisted on deleting Malwarebytes Free. Hence my concern about installing Malwarebytes Free on top of McAfee.
The instalkler now only objects to Malwarebytes and recommends uninstalling it, but you don't have to. That stalling at 'rootkit' means it was searching the drive for rootkits at that time and maybe it was having a hard timje deciding on something.
Saw that about the extension also. Went into Chrome and did not see anything related to the problem but deleted one extension I did not think I needed.
I think the strtsrv.com popup problem appeared because I got a popup about making Google my default search engine which I thought I already had. Thinking somehow Bing became my default search engine I clicked OK. I should have paid more attention when the next popup said Google was my default search and asked whether I wanted to change it. Thought Google was being quirky about asking that and said yes. It was early in the morning and I wasn't thinking clearly before the coffee.
So I went into Chrome tools setting and saw something else was the default search engine. ("conduit"?) Changed that to McAfee.
Still seemed to get the strtsrv.com popups. So as I said in my original post, I ran a full McAfee scan which detected nothing. Then deleted all my temporary internet files including cookies and browsing history. Since then I have not seen the strtsrv.com popups again.But it has been only a couple of days so far.
I have been a long time user of McAfee and have recommended it to many people. I am disappointed that McAfee did not clean this infection up during a full scan. Nor did it block the infection in the first place.