sidecar unable to connect deviced timed out

I have been trying to use Sidecar in the public betas of macOS Catalina and iPadOS 13.

I have a 2019 Macbook Pro, and a 3rd generation iPad Pro, so I know I have supported devices.

Both devices are on the same Wifi network, and both have Bluetooth enabled.

Both devices are logged into iCloud with the same AppleID.

Both devices have two-factor authentication enabled.

I have tried this both with and without a USB-C cable connection between the two devices.

The Sidecar preference pane in System Preferences does appear, and when I go into it I can see in the "Select Device" dropdown that my Mac can "see" my iPad Pro.

However, when I try to connect to it, I get the following after a pause:

I keep watching this page for troubleshooting tips, but none have been useful for me thus far.

FWIW, I have been a "good citizen" and reported my problems to Apple via the Feedback Assistant apps on both devices, so in case this is a temporary bug, I've reported it. I'm just asking here in case someone else has encountered this issue.

Edit: Eventually, Sidecar started working for me (sometimes) after some of the later public betas came out. I'm not sure exactly which version(s) of Catalina and/or iPadOS made the difference for me. So far it has worked without any timeouts in the final versions. I didn't need to downgrade and then re-upgrade as the submitted answer suggests, although I'm glad that has worked for some.

I had this problem setting up a new computer. For me, what fixed it was going into Settings > Accounts > iCloud and checking KeyChain.

It said I needed to update my account security and prompted me with a few security questions. This seems to have indirectly solved the problem; perhaps some minimum standard of security was not upheld and was causing quiet failure.

Unfortunately, I'm guessing that this won't solve everyone's problems as it seems to be a pretty generic message as mentioned above, just thought I'd add my solution to the pile for everyone who's going down the list and trying everything.

I suspect that this is a very generic error message and that not everyone who is experiencing it is encountering the same root cause.

I just experienced this error after successfully using Sidecar all day long at work.

After I came home, I logged onto my work's VPN to check on something and, after some amount of time, Sidecar disconnected. When I tried to reconnect it, I got the same "The device timed out" message.

On a hunch, I disconnected from the VPN (in the FortiClient app that my employer requires for VPN access) and Sidecar worked again.

Bottom line: using a VPN can cause this symptom.