Custom UTI does not work for iMessage in iOS 10 - ios

Question

I defined and used a custom UTI type for my iOS app for iOS 9. Now, after using XCode 8 and iOS 10, I cannot "open" the file, if it is sent via iMessage. If I tap on the icon, nothing happens, although the correct icon is displayed. If it is sent via E-Mail, I can still import it to my app. Is there a difference for mail and iMessage?
My info.plist declarations look like this:
<key>CFBundleDocumentTypes</key>
<array>
<dict>
<key>CFBundleTypeIconFiles</key>
<array>
<string>Icon-60#3x</string>
</array>
<key>CFBundleTypeName</key>
<string>My Voting Lists File</string>
<key>CFBundleTypeRole</key>
<string>Editor</string>
<key>LSHandlerRank</key>
<string>Owner</string>
<key>LSItemContentTypes</key>
<array>
<string>com.my-org.document.lists</string>
</array>
</dict>
</array>
and
<key>UTExportedTypeDeclarations</key>
<array>
<dict>
<key>UTTypeConformsTo</key>
<array>
<string>public.text</string>
<string>public.data</string>
</array>
<key>UTTypeDescription</key>
<string>My Voting List File</string>
<key>UTTypeIdentifier</key>
<string>com.my-org.document.lists</string>
<key>UTTypeTagSpecification</key>
<dict>
<key>public.filename-extension</key>
<array>
<string>mylist</string>
</array>
</dict>
</dict>
</array>
I also searched for a solution, but did not find something that works for me.
This stackoverflow discussion did not help me :(
Any ideas what changed or what my mistake is? Thanks in advance!