It did not feel like a problem caused by dust. Perhaps it was due to the small tolerances in the keyboard mechanism.
The B key would only work with a very firm press.
Because the laptop was fairly new, I assumed the problem was caused by a manufacturing defect with the frame. The problem was typically worse when the laptop was cold vs. hot.
If the problem is caused by dust (which I find hard to believe due to my issue after only 4 months of ownership) the problem must only need a small obstruction in the right place to cause a key to fail.
When the key failure happens, duster does not seem to help at all.
After the replacement, I have had no other failures. It's sad that a wonderful machine can be brought down with this terrible issue.
On a side note, I am very happy with the computer overall. The four thunderbolt 3 ports allow me to run my entire setup over one connection. I run an external RX 580 in an Akitio Node Pro to 2 4k monitors. MacOS UI design in my opinion feels clean compared to Windows currently and application support is fantastic compared to ten years ago!
Just thought I would offer my insight :)