I believe this could have to do with an add-on based on the issues I've seen in the past but I would need to see the log snippet for that error.
I've seen this before.
It can happen when you have a "project picker" field (this is a custom field type that ships with Jira off-the-shelf). If you use this field somewhere, it is really simple, the user creating or editing an issue gets to select an existing project from the list.But. Then an admin deletes a project (with an id of 13300). One that is selected in the field. As the list of projects is generated when the field is rendered, the project selected is not deleted from the field. You've now got a field with effectively invalid content.To check this, have a look at your list of custom fields and see if you have a "project picker"
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