I have done that procedure several times. Knowing about this problem, I made first an export of Calendar archive, just to be sure.
1. Force Quit Calendar
2. Sign Out in iCloud
3. Calendar is empty
4. Import my Calendar archive
5. As I have no connection, I have no Calendar updates between my different devices.
6. Sign in iCloud again. I do not understand the advice to sign in separately with Calendars and with Reminders, as they are both together just one option.
7a. First Calendar becomes blank again.
7b. Then pops up the message "Moving calendars to server account…"
7c. I have 8 different calendars in my Calendar application. First calendar is restored… (about 30 seconds)
7d. Second calendar is restored… (about 30 seconds)
7e. … and that's it. Only the message "Moving calendars to server account…" with a turning cilinder, pretending it is still in action. Once I left it like that for 2 days, in vain.
My only "solution": keep Calendar signed out of iCloud and enter each agenda activity on each of my devices. Isn't that ridiculous?