The issue with the newer versions of Nextcloud is, it does not work properly with existing server configuration.
I updated to the newer version 30.0.2 and it is giving me error HTTP 500. I was running the Nextcloud app smoothly in 29.0.8
you need to give us more details from your logs so we can help you.
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There is a forum support template for a reason. 
Also, see Troubleshooting: Internal Server Errors.