For me when I tried connect wifi_b827ebffffff_zzzzzzzz_managed_psk it always did the Error: ... In progress message. Presumably the app is just so aggressive retrying that I couldn’t get a chance to do anything between retries.
As further evidence for that, I tried rm -rf wifi_b827ebffffff_zzzzzzzz_managed_psk in the relevant folder, but despite apparently succeeding, the folder was there by the time I’d written ls.
(I didn’t know about the --remove command, perhaps it does something more complex than removing the folder, but that still wouldn’t work if my theory is correct)
I trust you’re going to give the --remove a try. Let us know how your theory got on.
I’m afraid that having already worked around the issue by cutting osmc’s WiFi interfaces out of the picture (see above), I’m not planning to break my system again to further reproduce the issue. I just wanted to post as much info as possible for the next person. If someone else has the issue hopefully they’ll find this and try it. If not, then maybe it’s not such a big issue. Thanks for your replies.
Recently I faced the same issue:
Used the installer on windows to install 2019.05-1 and configured the network with the installer for a Raspberry Pi 3. Other networks, and even attaching other wireless adapters didn’t succeed.
I reinstalled with the installer, without configuring any sort of wireless network. Then was able to connect through the settings on the Raspberry Pi directly.
I am not too familiar with OSMC, but if anyone needs me to debug this issue message me directly I can reset my device and do the whole log thing if needed. 
A log of this would be quite useful.
Is it possible you entered your WiFi key incorrectly?
Sam