Some users have run into syncing issues where no matter what they do, recent activities just won't send/resend to Runkeeper.com, even with a great internet signal. If you run into this issue there's a couple troubleshoots you can try that might get those activities accompanied by red triangles sent to our servers.
1.) If you have a category selected for those activities, try editing them and removing the category. Some users have had success resending them after that option has been deselected.
2.) If that doesn't work, look to see when the last time was that your app synced. There's a chance the first activity after that point may be corrupt. Check to see if you have notes or photos attached to any of the activities. If so, try deleting the notes and photos because they may be the cause of the corruption. Then try saving the activity once again.
Hopefully, one of these workarounds or both will get those activities sent to us, but definitely reach out to Support if you're constantly hitting this issue and we'll let you know when everything's fixed!