If it's happening randomly like that, it's likely that in certain conditions it isn't finding the org_id value to know which operating unit to use. If the org_id isn't set (or is set but to the wrong operating unit), then it can't find the organization and you get that error.
Check the Org_id profile option settings at all levels (user, responsibility, application, site, etc) to see where it is set and what it is set to. The most specific value is the one it will use (user if its set there, responsibility if nothing at the user level, application if nothing at the responsibility, and so on)
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