Note that when scheduled search does not have an owner, it is run by splunk-system-user.
The splunk-system-user seems to have a hardcoded quota.
Therefore, you'll need to assign an owner/user to the scheduled search and specify a role for the user. This is because there isn't a way to set a per-user disk quota so you'll have to edit the role to increase this limit. Here are the defaults from $SPLUNK_HOME/etc/system/default/authorize.conf: