Are you definitely looking inside the foo.Rcheck directory in the parent directory of package foo?
There have definitely been changes in the past few months in the packages that constitute devtools and their behaviour around this specific thing. So making sure all of that is very current, possibly even at a dev version, is also a reasonable thing to try.
I'm definitely not! I cannot find a directory named that anywhere
The build >check package is still producing the error, but if I run Build>install and restart it seems to work and I have the package available locally and documentation is correct