Let's reasons seems to be random selection of "not suitable for stock" and "out of focus".

If I really believed they shouldn't have been rejected, then I would NOT COMPLAIN, but first post the pictures online either here or shutterstock critique with a 100% zoomed in crop. 

This way I would be able to see what other people think and come to a decision: 1. My batch of photos really isn't up to snuff and I need to forget this batch and try harder for the next (keeping in mind the critiques given in the forum). or 2. The reviewer had no reason to reject all my photos and I will reupload a few at a time (3-5) amongst another batch.  If those 3-5 images are rejected again, I wouldn't bother with the rest.

It does happen, but not very often. I usually ignore it as other agencies accept from the same batch, perhaps a quick look over the reasons to see that 'yep they were just having a bad day'. It would take too much time to do anything like writing / dealing with a complaint compared to the benefit from doing that.

i agree with cclapper.
repeat: if all the sites rejected my images, i start to look hard at my submissions.
but if only this one site rejected them , then i say it's atilla and or relative . i would not lose any sleep on it.
if second time, the next batch images are approved by the other sites and still got rejected again by the same site, i will stop uploading to that site for a bit. since this is summer in most places, i would assume atilla found a summer job . and wait till summer is over to resubmit the same images to that site with the rogue reviewer.

I've never had a 100% rejection...  however, if I did, I'd just do what I've been doing since I got into this biz with rejected images.....   

If I felt the shot was up to par technically and I think the reviewer is full of it, I just wait a few weeks and resub it again... and heavy, heavy 90-some percent of the time... it's accepted on the next sub, rarely is it rejected the 2nd time.

However... I do take a humble look at every rejection... because sometimes, it should have been and I missed something in the image or in the tech aspects of it.

Melast....  If they meet the mark technicallly, wait a couple weeks, resub a few of them and see what happens. I've always had a problem with the rejection, "not suitable for stock"...  "says who?"
    I ALWAYS resub them, especially if  other sites have picked it up. Generally, the next reviewer wont think so. I can honestly say that some of our best sellers are those that had originally been 'not suitable'  LOL LOL. One in particular is a closeup shot of a brick sidewalk my wife took...it will reach  2,000 times sold later this year... LOL LOL not suitable..   =tom

what could be fixed I would fix.If it is to much work I let it go and shoot some more.
Also it depends what agency rejects the images.

What about the size of the batch?  4 or 37 ?