Hi - so I know this was a few years ago - but for you and anyone else who ends up here I believe I have a good answer to this problem: it’s actually the fan cooling the first layer extrusion down too fast so they are not able to adhere. Or, if you are in an uncontrolled space where your printer’s exposed, there may be too much temperature variation or air movement - over cooling things. The first layer above the raft is actually literally above the raft, so if the material dries too fast as it comes out of the nozzle it’s not able to adhere at all to the raft.
I have a Monoprice Voxel printer, which is enclosed, and I was having the same problem due to the fan.
What I did was set the fan to start up after the print had cleared the base layers, after the raft. In my case, this was at 1mm. I haven’t had a problem since. And, the first layer of print quality improved a lot. It’s not the “smooth finish” everyone seems to covet, but it’s way better.
If your printer’s not enclosed and you don’t have the fan on then I would suggest making sure there are no vents blowing air while you’re laying down the first layer.
Hope this helps you or anyone else who passes by here.