Probably the symbols are already properly loaded but you are not able to download them.
There is a discussion about this issue in apple dev forum but no solution was provided. Not yet. developer.apple.com/forums/thread/114655?page=2
It could be an Apple side issue but in the meantime you can use the dSYMs files on your local build machine.
When the Bitcode is disabled no Apple side recompilation has performed so the correct symbols can be found on local machine used for the build.
Xcode->Window->Organizer->Archives
Right click your build -> show in finder
Right click Your xcarchive file -> Select "Show Package Contents"
you should be able to find here the dSYMs folder
Some people say that if you don't have bitcode enabled, Apple will merely show, "includes symbols: Yes" without the Download link.
Some others say that they have to use Xcode's Organiser and click the "Download dSYM" which didn't give an error, but apparently did nothing (no files appeared anywhere??), but then in iTunesConnect, the blue link appeared next to "Includes Symbols Yes".
interesting discussion about it here
About Crashlytics: when building apps without bitcode, Crashlytics provides an upload-symbols tool that uploads your app’s dSYM local files every time that you need them for your app.
However, for apps with bitcode enabled, the process of uploading dSYMs isn’t so simple. Instead, you need to download updated dSYMs from Apple and upload them to Crashlytics each time you submit a new version of the app to App Store Connect.