Building on CI (started happening only in the last couple of days, perhaps when the Crashlytics pod was updated... Crashlytics (3.10.3)), I am now getting a segmentation fault when submitting the .ipa file to Crashlytics:
2018-06-28 20:11:39.789 submit Crashlytics: Crashlytics.framework/submit 1.3.5 (18)
carchive.sh: line 289: 10426 Segmentation fault
Where the carchive.sh step at that point does:
"${PODS_ROOT}"/Crashlytics/submit $GS_FABRIC_API_KEY $GS_FABRIC_BUILD_SECRET -ipaPath "$OUTPUT_IPA_NAME" -groupAliases "$GS_GROUP_TESTER_ID" -notesPath "$release_notes_file"
As per the linked issue, this is still an issue as of Crashlytics 3.10.4. Quickest workaround for now is to downgrade to 3.10.2 (pod 'Crashlytics', '3.10.2' in your Podfile and then pod update Crashlytics)
For reference, the error I was getting was super vague, even with the --verbose flag:
ERROR [2018-07-10 23:29:22.01]: fastlane finished with errors/Library/Ruby/Gems/2.3.0/gems/fastlane-2.99.0/fastlane_core/lib/fastlane_core/ui/interface.rb:141:in `user_error!': [!] 2018-07-10 23:29:14.457 submit Crashlytics: Crashlytics.framework/submit 1.3.5 (18) (FastlaneCore::Interface::FastlaneError)
2018-07-10 23:29:14.465 submit Crashlytics: Path to IPA manually provided: ./output/<redacted>/myApp.ipa
2018-07-10 23:29:15.658 submit Crashlytics: Path To App: /var/folders/<redacted>/myApp.app
edit: Works again as of 3.10.5 (make sure your crashlytics and fabric frameworks are up to date)