Maybe Leica can whitelist the url for your rtk subscription on their proxy? I'm having my rtk connection on the zeno drop in and out every half minute or so but I'm running a mifi because no carrier will activate the zeno's 3g modem. I've asked Leica about returning the zeno. They just didn't an answer. I guess I'm supposed to take that as a "No".
You can also try bypassing the proxy for your RTK service URL by adding it in the proxy network settings. That way, it should go through the default rather than the proxy. I had to do that for dropbox.com in order for it to work. See photo attached.