We've had many occurrences of test failed in EWS that seem unexplained. After looking at some buildbot logs, I think I see why.

https://ews-build.webkit.org/#/builders/70/builds/22723 is an EWS run for this PR: https://github.com/WebKit/WebKit/pull/6939. It's testing against 257312@main.

The archive is built in https://ews-build.webkit.org/#/builders/43/builds/31687, and appears to behave correctly. I verified locally that the cherry-pick logic does the right thing. The result is uploaded as https://s3-us-west-2.amazonaws.com/ews-archives.webkit.org/mac-bigsur-x86_64-release/88c31a9a.zip and downloaded OK by the tester.

Things go wrong when the tester checks out (trying to check out to 257312@main):
https://ews-build.webkit.org/#/builders/70/builds/22723/steps/5/logs/stdio

This does:
git fetch -f -t https://github.com/WebKit/WebKit.git main --progress
From https://github.com/WebKit/WebKit
 * branch                      main       -> FETCH_HEAD
Auto packing the repository in background for optimum performance.
See "git help gc" for manual housekeeping.
warning: The last gc run reported the following. Please correct the root cause
and remove .git/gc.log.
Automatic cleanup will not be performed until the file is removed.
warning: There are too many unreachable loose objects; run 'git prune' to remove them.
git reset --hard FETCH_HEAD --
HEAD is now at fc72928b66d9 [Live Range Selection] editing/pasteboard/cleanup-on-move.html fails https://bugs.webkit.org/show_bug.cgi?id=248673
git checkout -B main
Reset branch 'main'
git rev-parse HEAD
fc72928b66d943febf0a19941ced1d2b2e8f3496

which is checking out the current TOT, not 257312@main. Maybe FETCH_HEAD is unset?