From my experience it happens to any calculated fields using Percent as a type whenever a change is done to one or more data source schema even if the changes do not really affect the metrics type used to calculate the percent.
Just like in your example, the type will remain set to Percent, but it will suddenly be represented as if it was set to Number.
Refreshing the report doesn't help and all users will see it as a Number as well instead of a Percent.
Looker Studio appears to be at fault here and gets confused on what the field is even supposed to be. Percent type in the UI, but in reality a Number.
Ex: 23.33% would be displayed as 0.2333 assuming there is no rounding being done. Otherwise it would display 0 if rounded.
Reaplying "Percent" as a type on each calculated fields even though it is already selected in the dropdown will adjust it back to what it should have been in the first place.
I've generally avoided calculated fields unless I'm doing a quick prototype since they are a pain to manage in the long term.
To me it seems like percentage calculation created or already provided in the data source do not generally have as many problems as calculated fields do.
I can't remember any instances where a field would have been set to Percent and not be displayed properly when added to a table/chart.
If you are still looking for a work around, that would be my recommendation unless this relatively old bug is magically resolved at some point.
Never mind all of that, I was able to achieve the same visual bug this morning without using a calculated field.
As such, I don't believe there is a foolproof way around it that doesn't involve fixing this bug or always setting the type to percent after everything else is more or less set in stone on the report (hahaha).
LinkedIn
Twitter
