When there is no rules, suricata doesn't start when it is activated. When rules are then downloaded, it won't start either. The save button needs to be hit again and then suricata starts.
Fixed: https://git.ipfire.org/?p=people/stevee/ipfire-2.x.git;a=commit;h=00512a5ac800205a9f46cd0936909d5c921e6643