This is an accepted solution.
I have been doing some research and found out the cause, the Shopify Speed Report.
There are two other topics about this here; https://community.shopify.com/c/Online-Store-Speed/Online-Store-Speed-Report/m-p/908894#M390 or here; https://community.shopify.com/c/Shopify-Discussion/Council-Bluffs-visits/td-p/846963
Shopify runs the speed report using a Google Developer tool (the Google data centre is based in Council Bluffs, USA) which tests 3 pages, Homepage, a popular collection page and a popular product page. Shopify then compares this result to other similar Shopify sites. This test is run daily!
For some sites this is not a problem, but for some smaller sites this can screw with your analytics and conversion rate metrics. If you get 3000 hits a day, 3 extra visits is not an issue - it's only 0.1%. Not every site is as big as that. My site is small and sometimes gets tested twice in one day for some reason. If you use Google Analytics you can exclude these visits from the report. I do not trust Google with my data as I have caught them doing things with my data before, and these visits are messing with the analytics in Shopify.
I have raised this with Shopify Support a few times and each time they have "forwarded it to the Development Team" but it seems its not a priority for them.
So if this feature is negatively affecting you, make sure to reach out to Shopify and ask them to turn it off. If more people bring it up, it may get resolved sooner.
Better yet ask them to give you, the store owner, the choice of when or if your site is tested. Manually, Daily, Weekly, Monthly or Annually.
I’m certain it’s Shopify measuring the speed of the site, strange that support would deny this. It sounds to me like a default lvl1 response to the word "bot" without actually investigating (which is typical of my experience with their frontline support).
The hits started coming through when they introduced the speed measurement and was confirmed on another board as being from Shopify. This discussion has some more information on it:
How else are are they able to measure the speed of the store without crawling sites?
The hit's aren't impacting anything (and aren't showing up in Google Analytics) so there isn't a big concern with having 3 daily hits.
I just found these posts and realize I am not alone in receiving these 3 simultaneous "visitors"! How did you find out where they come from ? I'm in Canada and all I can glean from this is that all three are from the U.S. and all are from mobile devices. I reported this to Shopify but was basically told it was nothing to worry about. I did not get an explanation.