Você precisa escapar do sinal de porcentagem em seu comando com uma barra invertida: \%
, caso contrário, ele será interpretado como o fim do comando.
De crontab (5):
The command field (the rest of the line) is the command to be run. The
entire command portion of the line, up to a newline or % character, will
be executed by /bin/sh or by the shell specified in the SHELL variable of
the crontab. Percent signs (‘%’) in the command, unless escaped with a
backslash (‘\’), will be changed into newline characters, and all data
after the first ‘%’ will be sent to the command as standard input.