excel skips to another workbook for no apparent reason

We have been using the registry change and the basic symptom has disappeared. I don't know what you're referring to about using file explorer from within Excel. 

When researching the registry edit "solution" linked on this thread

https://support.microsoft.com/en-us/help/3165211/how-to-force-excel-to-open-in-a-new-instance-by-default

Microsoft notes, "This method works only when you use the Excel icon to open the application. If you use File Open within the Excel application or double-click a file in Windows Explorer, the files will still open in the same instance as designed"

That means this "solution" requires us to open the separate instance of Excel from the start bar and then use the File > Open > My computer > Browse, then select our internal server, THEN file down through our job sorting system (another 6 layers) to finally arrive at the folder with the file. Simply double-clicking the file within the File Explorer window I already have open for the job I'm currently working on does not let Excel open a separate instance. This is not a viable solution for me. I spend less time (albeit a marginally greater amount of frustration) simply dealing with the problem.

It's ridiculous and unacceptable to require users to employ a cumbersome workaround for an issue that has existed for over 3 years.

I have been running Excel in seperate memory spaces to try and avoid this issue for a number of years now by just doing Win+r and runnimg excel.exe /x.

Problem persists because I do need to have a number of sheets open in the same memory space for most of my work, so it is not a fix at all.

Something new however yesterday, I had a single excel sheet open and it would freeze when entering data or moving around. The only way to fix it was to change the tab on the sheet or resize the window. This looked to like the same issue but when a single sheet is open. 

For a flagship product it is very poor that MS just ignores bugs like this. Service like this only happens when you have a near monopoly status. So frustrating.

I see the solution of using a registry edit create separate instances of Excel, but I also see that this solution only works when you use the file explorer from within Excel. When your files are 6-7 layers deep in the server this is a big time-waster. 

We have been using the registry change and the basic symptom has disappeared. I don't know what you're referring to about using file explorer from within Excel. This seems to have affected every Excel instance however launched. We no longer flip from file to file, although there appear to be some other side-effects (presumably, related to things that Excel was able to do with multiple sheets in the same instance). 

I agree that the lack of any apparent action or acknowledgment in this flagship product is frustrating. But it seems pretty much par for the course in the software biz today.

I can tell you now, this will not fox the problem. I have been running excel in different memory spaces for years and still get this problem. 

It may work if you keep every excel sheet in its own instance of excel. The moment you open up two sheets in the same memory space the problem comes back.

Try the workaround I posted on page 8. Hope this helps.