i have had the same problem with my M1 and chased myself around in circles with joining my home wifi network failing time after time. on occasion when it did connect to the wifi, it would not complete connection to the internet, or if it did, it would try and update, fail, and then loop back to setting up the wifi.
i had been using the android app, and tried the mac app on my mac laptop with no difference.
i took a hint from tstaten's post above and set up my iphone as a wifi hot spot, joined my mac to it, and then went through the sling box setup selecting the phone's hotspot wifi as the connection for the sling. the setup worked as it should, including downloading the update, and re-joining the phone's hotspot after the update. once i finished the setup, i tested the ability to connect and view using the mac's app, still using the phone's hotspot as the internet connection.
i then followed the on-screen instructions to reset the wifi on the sling box, pressing and holding the WPS button on the sling until the wifi light blinked three times, then went to steady blinking. i then shut the phone's hotspot down, and rejoined my mac to the home wifi and repeated the setup process from the mac. this time the sling joined the home wifi and the mac app connected up and everything works now.
i run WPA2-AES encryption on the wifi network. i did not test trying to downgrade the encryption and seeing if that fixed the original problem, but my suspicion is that the firmware as shipped with the M1 has trouble with certain wifi encryption modes, and the new firmware fixes that. for whatever reason it was happy enough with the phone's hotspot wifi that i could get the update. i dont think this is really an answer to everyone's issue, but i was able to get it to go doing this.
it would be great if someone from sling would weigh in and help, since had i not gotten this going with that final attempt it would have gone back and the box gotten a low review on amazon.
good luck! hope this helps.
PS - i tried to post this in the original question asked by one of the members, but the blog site won't seem to accept the reply.