So, 117 images online with no rejects but latest 2 are rejected.  There doesn't appear to be a reason given and the images concerned are certainly better than many of those accepted.  Do folks in general experience a degree of inconsistency here / are there any particular types of image that are more likely to get a reject?

If you are on your history page, look at the bottom right of the screen where your totals summary is displayed. Click on the rejected images count and you will get a display with every image and on the right the reason for rejection (they always give reasons for rejections). Only had 1 time without and that was when my total upload was corrupted.

Further, they are probably one of the most consistent sites in respect of reviews I submit to.

Ah...  My bad, showing as royalty free rejects but accepted as editorial 

The reviewer may have mistaken the figure for a real person without a model release - how does one contact support - site mail?

It caught me also the first time they accepted my images under editorial.

Look under the menu (bottom of screen) under support. The words "Contact" is a hyper link to support page