rust-analyzer: Server gets stuck, apparently due to broken Cargo metadata

So I’ve run an issue a few times now over the last few weeks where my cargo check commands in the terminal get stuck for a very long time (sometimes minutes) blocking on “waiting for file lock on package cache”. I just had this happen to me again, and decided to dig in a little. I now think this might be happening when RA tries to read my Cargo.toml file just as I’m editing it. This gets it into an error state, like this:

[ERROR rust_analyzer::reload] failed to load workspace: Failed to read Cargo metadata from Cargo.toml file /Users/djc/src/ids-rs/Cargo.toml, cargo 1.47.0 (f3c7e066a 2020-08-28): Failed to run `cargo metadata --manifest-path /Users/djc/src/ids-rs/Cargo.toml`: Error during execution of `cargo metadata`: error: failed to parse manifest at `/Users/djc/src/ids-rs/nominl/Cargo.toml`

Caused by:
  could not parse input as TOML

Caused by:
  newline in string found at line 24 column 96

[ERROR flycheck] Flycheck failed to run the following command: "cargo" "check" "--workspace" "--message-format=json" "--manifest-path" "/Users/djc/src/ids-rs/Cargo.toml" "--all-targets" "--all-features"
[ERROR rust_analyzer::main_loop] cargo check failed: Cargo watcher failed, the command produced no valid metadata (exit code: ExitStatus(ExitStatus(25856)))

After this, it looks like it eventually recover, but it’s taking very long to do so (maybe some timeout?) – and all the while it appears to be holding the package cache file lock.