I am having the same issue. I called support and you are right they don't care. They insisted that there was another user. When I said that was impossible they still insisted and left it that. Very frustrating. I switched it to a roku stick which seems to have fewer conflict errors. I hope they fix this soon.
They won't fix it. I now use only one Roku, but their app still periodically, at random, thinks there is another user somewhere, which there isn't. However I also bought the latest Fire Stick, hoping for better results and even though their app loads, it doesn't work and so far still doesn't, and they know it.
Seems they don't frequent this forum either.
I have called support about this issue (I have several Slingboxes) but all I can get from support is that there is a "conflict" between my two Roku3's on the same network. There is no conflict. Either Roku works fine on other channels.
What happens is that if there is more than one Roku online then slingplayer sees them both but always thinks that there is another "authorized user" logged on, "disconnect, yes or no?". Disconnecting (yes or no) still keeps the stream working but always reverts to the phone, meaning that any channel change must be made on the phone and can then be connected back to the Roku, but will result in the same message and process until one wants to change channel again; all of which is a pain in the ***.
One solution is to unpower one Roku in the house, and the phone because the latter still pretends there is another user even if there is only one Roku powered up if there were two previously.
The better solution is not to use the Slingplayer option to cast to the Roku at all, but to use the Miracast function on the phone instead. The only difference is that the latter leaves the screen on at the phone (but not sound) which doesn't matter much, but it does seem to prove that the Miracast method doesn't have the Slingbox app fantasy of an imaginary user, and suggests that Slingbox support really don't know what they are talking about but just like to blame some other software when theirs doesn't work. Another advantage with Miracast seems to be that there is less "buffering" when on a slower network; in fact almost none, unlike with the Slingbox app even though the stream comes from a Slingbox.