No. There were a lot of unrelated replies posted between mine and the one I was replying to, so I should add some clarification. I am having no issues whatsoever after changing the URL as indicated in my earlier reply. I am using multiple calendars, but they are all from the same ownCloud account.
The problem @Dude11 is experiencing appears to be multiple issues. One of which I experienced with the OAuth application interfering with Thunderbird (Lightning) access to the official calendar URL. The other is accessing calendars from 2 accounts, which is something I don’t employ, so I have not experienced it.