SharePoint Online - When an existing item is modified - MMS Column Failure - Bad Gateway
Steps to reproduce:
1) Add 'When an existing item is modified' trigger to a new Logic App or Flow.
2) Target list has MMS column where internal name is different to display name - a display name with spaces ('Company Name'), and an internal name without ('CompanyName').
Result: On run, Bad Gateway: status 502, message "Unknown Error", source "<URL>/_api/SP.APIHubConnector.GetUpdatedListItems".
Does not appear to happen with other types of field (e.g. text, lookup). Does not seem to depend upon term set title.
Workaround: create columns where the internal name and display name are the same.
Why this is bad: it encourages terrible information architecture and column naming. It prevents adding Flows to lists and libraries where good column naming has already been enforced. In SharePoint, after you create a column you can't change it's internal name. The workaround in many cases means making the display name look ugly.