Same problem, but only downloading individual plates. When it occurs the Plate label in the right Windows appears white instead light Green
On problem downloading list of all plates

We initially found this hard to reproduce as we couldn't get it to happen on our main testing PC. We've done so now though. I've posted a beta at the link below. Please confirm the issue is resolved, and we will get a new general release out later in the week.
http://www.skydemon.aero/start/beta.aspx

That beta today fixes it for me, thanks.  I successfully downloaded probably a dozen plates without problems whereas before it would loop every the time downloading plates (that is, any plate not already downloaded). 

And thanks for getting out the new release verson 3.4.1 (which fixes the problem) so quickly!