cargo-llvm-cov: llvm-cov report - no filenames specified (failed only on windows and works on linux)

I’ve been trying to add coverage for the Rust part of a combined Python and Rust project. I’ve got it working for our linux CI builds, but trying the same thing for Windows is leading to this error:

Run cargo llvm-cov report --manifest-path=rust\Cargo.toml --codecov --output-path codecov.json -vvv
  
     Running `C:\Users\runneradmin\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\llvm-profdata.exe merge -sparse -f D:\a\kolo\kolo\python\rust\target\rust-profraw-list -o D:\a\kolo\kolo\python\rust\target\rust.profdata`
     Running `C:\Users\runneradmin\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\llvm-cov.exe export -format=text -use-color=0 -instr-profile=D:\a\kolo\kolo\python\rust\target\rust.profdata -ignore-filename-regex \\rustc\\[0-9a-f]+\\|^D:\\a\\kolo\\kolo\\python\\rust(\\.*)?\\(tests|examples|benches)\\|^D:\\a\\kolo\\kolo\\python\\rust\\target($|\\)|^C:\\Users\\runneradmin\\\.cargo\\(registry|git)\\|^C:\\Users\\runneradmin\\\.rustup\\toolchains($|\\)`
error: failed to generate report: process didn't exit successfully: `C:\Users\runneradmin\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\llvm-cov.exe export -format=text -use-color=0 -instr-profile=D:\a\kolo\kolo\python\rust\target\rust.profdata -ignore-filename-regex \\rustc\\[0-9a-f]+\\|^D:\\a\\kolo\\kolo\\python\\rust(\\.*)?\\(tests|examples|benches)\\|^D:\\a\\kolo\\kolo\\python\\rust\\target($|\\)|^C:\\Users\\runneradmin\\\.cargo\\(registry|git)\\|^C:\\Users\\runneradmin\\\.rustup\\toolchains($|\\)` (exit code: 1)
--- stderr
No filenames specified!

I have confirmed that the .profraw files are generated and are in the directory I expect them in:

Run dir rust\target
  

    Directory: D:\a\kolo\kolo\python\rust\target

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           8/11/2023 10:56 AM                debug
-a---           8/11/2023 10:55 AM           1048 .rustc_info.json
-a---           8/11/2023  9:00 AM            177 CACHEDIR.TAG
-a---           8/11/2023 10:56 AM        2377336 rust-1720-9197467843878644390_0.profraw
-a---           8/11/2023 10:57 AM        2377336 rust-3488-9197467843878644390_0.profraw
-a---           8/11/2023 10:57 AM        2377336 rust-4996-9197467843878644390_4.profraw
-a---           8/11/2023 10:57 AM        2377336 rust-5820-9197467843878644390_4.profraw
-a---           8/11/2023 10:57 AM        2377336 rust-5936-9197467843878644390_0.profraw

I’m at a loss how to further debug this.