I've done some digging to figure out the exact issue:

• In the last commit, you switched to using a Hash for code sign, and thus return a hash for the identity option instead of the string (see f1b226a)
• In the entitlements utility, if ElectronTeamID isn't in Info.plist, you use opts.identity to parse out the value from the identity option (see https://github.com/electron-userland/electron-osx-sign/blob/master/util-entitlements.js#L53)
• Being as the identity value is now a Hash instead of the identity string, this fails and causes an incorrect value to be added to com.apple.security.application-groups array, even if the correct value already exists

One other note: when using electron-builder, the identity is actually passed as an option, so it would probably to use that rather than looking in the Info.plist