Frustrating BVOH printing issue  

Frustrating BVOH printing issue

I've been trying to print a model that has a 90 degree overhang using soluble interface supports with verbatim BVOH, and I've been seeing the strangest problem. If I print just one of these models, it's a small disc similar to the ones used in staples arc notebooks, the BVOH works perfectly, it prints well, sticks to the pla support material beneath it, and makes a lovely interface. But if I print 8 of these (one set for what I'm doing), the BVOH on the first layer of the interface prints well on the first printed disc, but then gets progressively worse until between the 6th and 8th disc, the BVOH won't stick to the pla beneath it at all.

Here's how the model is arranged in Prusa Slic3r, you can see the rim touches the bed, and halfway up the disc there's a horizontal section that needs support.  Here I have support enforcers so that I only get supports where I need them:

It slices with the green pla as support material, up until the BVOH interface, which I have set up to not have any gaps, because of the detail on the leaf design in the center of the disc:

When I print one, it comes out beautifully:

But when I try to print 8 at once, this happens every time:

The disc directly to the right of the wipe tower is the first one to print, and prints the "most normal".  Then it goes counterclockwise down and around, until the one on top of and on the right side of the wipe tower is the last.  The BVOH gets progressively worse, but the first 4 print relatively well.  You can see on the fifth one, to the left of the wipe tower, the issue starts to get really bad, until the 8th disc (and sometimes the 7th) refuses to stick to the PLA beneath it, and usually gets all balled up and sometimes sticks to the extruder. 

I'm using Esun PLA+ for the green, and Verbatim BVOH, with the default settings for these filaments.

At first I thought it might be an airflow issue, as my printer is on a table next to the door of my room, but I have blocked off the airflow from the left and back of the printer, and it still happens. 

Any ideas on what is going on here?