Ok so this is going to be a very quick post. I’ve experienced this bug for some years now. AND I honestly thought I must have been hallucinating or something. It must be me doing something wrong. What did I break? Until I finally stumbled on something…
So the scenario…
You have a couple of scorecards with metric data on them. It might look something like this but probably less boring. (Think LESS Mark Zuckerberg MORE Dwayne Johnson).

Everything is going as smoothly as as smoothly as a squirrel hosting a TED Talk on acorn storage. And you decide “well now it’s time to blend…”
AND all goes well. Why shouldn’t it?

AND for best practice you rename the blend… because you’re forward thinking like that and you’re not a blended data (iteration 1000) hoarder.

AND maybe set the percentage to just 1 decimal places…because you’re not a numerical psychopath (not anymore anyways).

ALL looks great. But then… You add another simple scorecard. Not blended just another metric or maybe a metric with event count using an event filter name. Standard stuff.
AND this happens:

Where the hell did my numbers go? And who kidnapped my %!
I’ve tried this so many times and gone around in circles. AND ended up at the same place!
But finally just by chance I happened to find a way to fix it….
You don’t have to delete the blend
You don’t have to start again
You don’t have to cry into your cereal like it’s the only one who understands you.
ALL you have to do is to go to the blended metric
Then go to Data Type

Then change the “Percent” data type to number (or anything you want)
Then hit Apply

“Wow I have numbers now right!”

And then change this back to percentage again (and APPLY)
“There he is there’s my buddy!”

AND hey presto done!
Now be warned, this might happen every time you add a new metric after a blended data source. And this might only happen when you do a quick blend by selecting two data sources and right clicking. I haven’t tested it the other ways.
BUT all you have to do is to follow the method above each time and your scorecards should work again. I think it’s just Google Looker Studio’s method of giving your fingers that bit extra workout instead of being inconsiderate and making them lazy by only clicking it once.
Let me know what you think in the comments. Did this work for you? Have you experienced something similar?
Happy Looker StudiohOHoh!ing!