GET /rest/atlassian-connect/1/addons/$addonKey intermittently returns 403
At about 2019-06-02T08:59:00.660+0300 our app received response code 403 from GET request to /rest/atlassian-connect/1/addons/com.almworks.jira.structure. There were in total 18 such requests with this response at about the same time ( 2019-06-02T08:59:42.336+0300 to 2019-06-02T08:59:53.856+0300, until the situation resolved itself. All requests were to the same Jira instance.
At the same time, there were other failing requests to the same Jira instance: we were getting 503 Service Unavailable for /rest/api/2/search (about 40 requests). This, along with ACJIRA-1838, leads me to think that this is due to the service misrepresenting some internal 503 as 403 to the end user.
This affects us as a vendor company because we've alerts enabled for 4xx responses from Jira, since this status implies that we have a bug. In reality, in such situations we should get 5xx responses (503).