Experiencing the same thing of Nextcloud becoming unresponsive. New Nextcloud install (30.0.0) on Ubuntu with Office Online integration app (2.2.1). Also happened on version 29.0.x. Disabling app restores working Nextcloud instance.
[no app in context] Fatal: Capabilities of OCA\Officeonline\Capabilities took 45 seconds to generate.
GET /apps/files/
from xxx.xxx.xxx.xxx