Assuming you have 3wks data for both the solar and use feeds, I suspect this might be caused by the changes made to the core feed api’s. I do not know that for sure, but the code used to work and it it’s now possibly not returning the right number of days data, that is too coincidental to overlook.
Some background in the “Could not do basic feed API query - #12 by CDuffy” thread.
You could try commenting out this line in emailreport/emailreport-module/emailreportgenerator.php
as it looks like there has now been a “+1 day” added to the feed api so maybe there are 9 days being returned that the fail the “if != 8” tests.
otherwise you could try editing those "8"s directly to see it you can workout how many datapoints are being returned
just be sure to use the same number for those last 2 otherwise the next check will fail