Field Parameter display values appear twice when published to online

Hi all, 

My team is using Field Parameters to create a Pivot Table-esque experience for the user. In Desktop, we have something like this: 

Desktop: Working as expected. No value duplication.

We're publishing the reports via a CI/CD pipeline (due to company policy), rather than just clicking "Publish". When the reports are published via this CI/CD pipeline, there is a strange duplication bug:

Online: Field Parameter values are duplicated on the slicer buttons.

(Blacked out most column / row values, but they are ALL showing duplicate values, as the image suggests.)

As you can see, on the online version, the value appear on each button twice... no idea why! Is this a known bug? I know Field Parameters are relatively new... has anybody else come across this before?