As long as I'm logged in, the tests carried out in the auto test are shown in the "My Results" page, even if the test gets stuck or I inadvertently close the browser ...
One way to help make the Auto test results stand out is to choose an identifier, e.g. "Home" if you don't use that identifier with manual tests. This way it shows the associated icon next to the results on the "My Results" page, so you know which were from the Auto test.
If you were logged out while running the Auto test, go back on the connection you ran the auto test and bring up the "My Results" page. There is good chance it will show the results from the partial run that were carried out, assuming your IP address did not change since running the Auto test.
If the results are not shown, try this with your computer connected to the ISP you ran the Auto test on:
Go into the "Database" menu, then into "My Detected Info" and then into the "ISP: (your ISP)" (4th listing)
Click the button "Speed Test Log".
Change the "25 results/page" option to something like "250 results/page"
Look through the date & times on the left column to see if any match up with the time you ran the Auto test and continue page by page until you do. This is generally pretty straight forward unless you've using a popular ISP like BT Broadband.
A tale-tale sign you've found your results is where the "ConnectID" column has a matching figure at roughly each time interval you chose, e.g. each 30 minute time period has the same ConnectID for a 30 minute interval test.
Once you're fairly sure you've spotted it, click that ConnectID figure and you should have the series of test results from that Auto test.