When the UI is localized, formula names in Spreadsheet documents are translated. E.g. when the UI is in Spanish, the function SUM() becomes SUMA(). This is confusing for many users who expect function names to be consistent across localizations.
The desktop version of LibreOffice has a checkbox under Options --> LibreOffice Calc --> Formula to Use English function names. I haven’t been able to find this option in Collabora, is this configurable?