Out of nowhere formulas are supposed to be invalid.

[Jurian]

I get errors in my formulas, that used to work. Looker Studio says they are invalid.

[sam8]

It's working OK for me! 

If you create a new field with the same formula, do you get the same error? Or is this only for existing formulas?

[Jurian]

This was an existing formula. The formula does work, only the error shows up at formulas which are perfectly fine. Sometimes there are no errors, sometimes there are. This seems like a bug.

[LucienTIW]

It might work for you, but that's the thing.
It's a roulette!
One day you open a Looker and all your formulas work, the next they dont. You change them, they work again although they say the formula is invalid!

Very time consuming and frustrating, it's a bug that needs fixing.
Surely most users believe that they actually wrote an error, but the formula is correct, like in the example given.

[LucienTIW]

It's happens ALL THE TIME in our multiple Lookers.
It is so insufferable we're considering opting out and going for another tool.
The hours I spend recreating, modifying, reconnecting is too much.

Sometimes these fix the issue, sometimes not!
It drives me nuts!

[simon-ithaque]

I have the same issue that appeared in existing formulas with the error message saying that the formula is invalid. I try to write the formula on a new one and the issue is directly present. I also tried to simplify the formula to return a simple numeric value and the same error continues.
Do you have any solution ?

[LucienTIW]

The best fix I found is to recreate the calculated field from scratch...

But sometimes it says the formula is invalid, but it actually works!

[Uke]

I had the same issue and realized that some calculated fields where still appearing in the connection settings even though I deleted/modified them in the Data Pane.

I was able to solve this issue by going to the All Fields button when you are typing out the formula. Here you may see previous fields that you worked on that may cause the issue. I deleted these repeated fields by clicking on the three points and removing them.

After removing them I had no issue adding the same formula as before.