Ever seen an issue with an Office add-in where the it sometimes won't load and instead opens itself as a blank page in a browser? This sometimes happens to one of my clients who installed my Outlook add-in. When they open it, it immediately pops open a webpage in their browser that first redirects to a Zscaler link, and then directs to the add-in link, which is https://office-eu.testingcenter.net/ReportPhishing.html?killphish_instance=db3791d4-ff2e-45b5-8efe-b767d4e85004&et=#. I'm not sure if the issue is caused by Zscaler itself, or Microsoft, or with the add-in.
Most of the time, the add-in loads fine for this customer. But maybe 2% of the time, this odd behavior occurs. I've attached a screenshot of what the add-in normally looks like when opened as well as a screenshot of what it looks like when it opens the page in a browser. I'm not seeing any errors in the JS console or on my backend related to this. This issue is occurring on OWA, Outlook desktop, and the new Outlook (PWA).
The client had to add the add-in URL to their Zscaler allowlist.