Hi @Ashley Hicks ,
Well, the categories randomly stopped working today
Would you please clarify a bit more about the issue symptom? Do you mean all the categories randomly disappeared or anything else? If possible, you may remove any personal information involved and share a screenshot about the issue so that we can understand better about the situation.
By "use the web browser form of Outlook for multiple work email accounts", are you using shared mailboxes?
Is it affecting other users in your organization?
Besides, I'd like to suggest checking in Outlook client as well and see if categories work there.
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