Here's a failures log:
https://uberchromegw.corp.google.com/i/internal.bling.main/builders/iphone9-device-x64/builds/9237/steps/ios_web_shell_egtests%20%28iPhone%205s%20iOS%209.3.2%29%20on%20iOS-9.3.2/logs/ContextMenuTestCase.testContextMenu


And sample output:
Exception Name: NoMatchingElementException
Exception Reason: UI element cannot be found.Exception with Assertion: {
  "Assert Criteria" : "assertWithMatcher: notNil",
  "Element Matcher" : "(((kindOfClass('UIView') || respondsToSelector(accessibilityContainer)) && ancestorThatMatches(kindOfClass('_UIAlertControllerView'))) && interactable && ((kindOfClass('UILabel') || kindOfClass('UITextField') || kindOfClass('UITextView')) && hasText('Copy Link')))",
  "Recovery Suggestion" : "Check if element exists in the UI, modify assert criteria, or adjust element matcher"
}

Disabled test, so setting RBB for next milestone (M58)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5ea36c973a46c98262c61b5e1d7c8dd86038c857

commit 5ea36c973a46c98262c61b5e1d7c8dd86038c857
Author: baxley <baxley@chromium.org>
Date: Wed Feb 01 23:14:55 2017

Fix context menu web shell EarlGrey tests.

Verify links are visible on the webview before trying to long
press them. Enables testContextMenu.

BUG= 687546 

Review-Url: https://codereview.chromium.org/2674473002
Cr-Commit-Position: refs/heads/master@{#447638}

[modify] https://crrev.com/5ea36c973a46c98262c61b5e1d7c8dd86038c857/ios/web/shell/test/context_menu_egtest.mm

This was a different context menu problem where it attempts to longpress the link before it is visible. Waiting for the link to be in the webview seems to have fixed it.

I was able to repro it on a iPhone6 (or 6s?) running 9.3.5.

Adding this delay seems to have fixed it. Please re-open if it persists.