I'm having a similar problem.
My wifi has a higher bandwidth than my internet subscription allows. When I upload many files or large files Plastic floods the internal wifi to the maximum speed, which causes timeouts because the data is not sent out at he same speed. And eventually the wifi connection will drop and I get a timeout message stopping the upload.
I don't think using multiple threads will make a difference, this will still use the internal speed to the max, right?
How can I limit the upload speed in Plastic and Unity? I don't mind that uploading will take longer.
Thanks.