I tried to upload a CL with git cl upload -d, and after a long delay (half a minute? more?) I got an error back: Failed to create a change. The more detailed error message was commit(s) already exists (as current patchset)).

It looks like it did create a CL, but it did not start try runs. The CL in question was https://chromium-review.googlesource.com/c/chromium/src/+/1095336 (I started trybots manually).

Full input and output below:

bratell@bratell-linux:~/src/chromium/src/chrome/browser$ git cl upload -d
Running presubmit upload checks ...

Presubmit checks took 1.6s to calculate.

Presubmit checks passed.
 third_party/blink/renderer/core/frame/performance_monitor_test.cc |  8 ++++----
 third_party/blink/renderer/core/loader/idleness_detector_test.cc  | 12 ++++--------
 2 files changed, 8 insertions(+), 12 deletions(-)

remote: Processing changes: refs: 1, done            
remote: (W) 17ef5e5: commit subject >50 characters; use shorter first paragraph        
To https://chromium.googlesource.com/chromium/src.git
 ! [remote rejected] 17ef5e5ec9c0a114d96fd263ed9ccb364f6d850a -> refs/for/refs/heads/master%wip,m=Initial_upload (commit(s) already exists (as current patchset))
error: failed to push some refs to 'https://chromium.googlesource.com/chromium/src.git'

Error after CL description prompt -- saving description to /home/bratell/.git_cl_description_backup

Failed to create a change. Please examine output above for the reason of the failure.
Hint: run command below to diagnose common Git/Gerrit credential problems:
  git cl creds-check