I had the issue with the doubling with the b key as well.

Mine was out of warranty, so I fixed it myself.

Failed: compressed air Failed: cleaning under the key.

Success (but not recommended) I removed the key, then pulled off the glued membrane. Cleaned all with 90% alcohol. Took a new membrane (but you might be able to use old) and used E6000 and a toothpick to glue it back. Replaced butterfly and key.

Not a good solution, but it worked.

It looked like the contacts were getting coated and not making good contact? Perhaps heat?

Best of luck.

I am not confident in my ability to do that but it's good to know there is a solution if I get desperate enough. My mechanical keyboard is saving my life right now.

Any ideas on how to get Apple’s attention on this issue welcome! Was wondering if there is any value on setting up a simple site where people can comment if they’ve had issues, just to help illustrate the scale of the problem...

I'm sure if one of us creates a site and shares it here it'll gain traction. I like clever domain names, so I just registered mbp.wtf from Gandi. If you have recommendations on a lightweight commenting system, I'd love to hear it!

I can crank out a site fairly quickly but I also want it to be as low-maintenance as possible.

Ha I like the domain! Will have a little think and get back to you :)