I have a few Macs running my app using cloudkit. My Macbook Pro is the only one where I am running the latest Catalina beta, 10.15 Beta (19A526h). It is able to access the cloud database fine, but does not receive any cloudkit notifications. I think this may be due to cataling as the other Macs get their notifications fine.
Still having this issue with the beta OSX after getting the latest XCode Version 10.3 (10G8)
I have filed a bug with Feedback Assistant