Import only imports the first 100 elements of the spreadsheet. According to the support, it depends on a restriction in Google Spreadsheet
Anyone has any ideas for a workaround?
You may try
This is the link from the Google SpreadSheet when one does a File -> Download as -> Comma-separated values (.csv, current sheet)
which is the source attribute on an iframe on this web page. Splicing that iframe src with the base URL, removing the gid adding usp=sharing. The final URL seems to import the data you want. To do this for any other similar google doc report explore the DOM with your browser's development kit or examine your network traffic to see where the download as links take you.
It worked even better with my real data when I replaced the csv value for the format parameter and parameter to Import with xlsx. Date and structure was more like the straightforward import of the direct sharing link.