To reproduce, create this test project:
.
├── Cargo.toml
└── crates
├── foo
│ ├── Cargo.toml
│ └── src
│ └── main.rs
└── README.md
Commands to generate the test project
mkdir issue
cd issue
printf "[workspace]\nmembers=[\"crates/*\"]" > Cargo.toml
cargo new --bin crates/foo
echo what > crates/README.md
Then run: x build -p foo