Google Sheets - INDEX() and QUERY() work on some cells, but not others

Question

A simplified spreadsheet showing the issue is available here

As you can see on the sheet, columns I through M all have sporadic failures in them. I'm unable to figure out why these fail. The use of QUERY() was suggested in this question and at first I thought it was the answer, but then I started seeing failures as I filled it down my sheet.

I appreciate any insight as to why these failures occur.

OK WTF - literally as I was about to press the POST button, I checked the sheet one last time and all but ONE error are now gone. The only remaining error at this moment for me is in cell I4. However in my original larger sheet, the errors persist as they did before I made this cut-down version.

And now about a minute later, even that one error is gone. But then I reloaded the page and the errors are back, identical to when I started this question. Same is true on my real sheet. I don't know what to make of this... I truly don't.

Answer 1

The only sure-fire solution I've found, after days of scouring the web and trying everything I could find, is to use ImportXML. It appears to work consistently every time, while importhtml() fails quite frequently. Here is the tutorial I followed, it's actually incredibly easy to use and works far better!