Limiting the number of columns to 30 is just a recommendation, however there shouldn't be any issues while uploading >30 columns.
As you have mentioned that there are 8+ files to be imported, are you trying to upload next file before the old file has finished processing? If multiple files are uploaded for the same variable and report suite, the old file stops processing in favor of the new one. If uploading classifications using multiple files, wait for confirmation that existing files have finished processing before uploading new ones.