RESCRIPT error: Download did not finish. Reason unknown

In that case, why not use the LSU from SILVA? See here:

You can use qiime rescript get-silva-data to download the latest v138.1 LSU database. Just set --p-version 138.1 and --p-target LSURef_NR99 or --p-target LSURef. You can follow along the in the above linked tutorial to perform further filtering and curation of the reference database.