Hi,
I think that you should restart bro and here is why...
Your data are appended but the old ioc's that are not relevant anymore are not removed. One day you may have a lot ioc's to check against the traffic so you may experience problems like packets drops and etc...
We had this issue so this is why we decide to restart bro once day just to avoid that problems...
Sure just pick up time that works for you best!
Regards,
Audrius