I would say (based on your log):
++ ftp -i -n dedibackup-dc2.online.net
+ listing='Trying 188.8.131.52...
-rw-r--r-- 1 1001 ftp 12672814 Jul 7 07:57 GSW-05-07-2016.dmp
that very first line caused a shift, probably by two, you need to check that.
in that case you need to adjust all the "expr $FNO + <number>
" expressions by incrementing that number - everywhere. But it is only a guess and you need to check if that really