@kennett Never heard of that issue and I haven’t seen any delays in sync with my Rival. Definitely reach out to Wahoo support to get some help. You might need to reboot the watch but they can let you know the best course of action.
I know this is an old post, but I had the same problem syncing my Elemnt Roam. I simply re-paired the Elemnt app with my Roam and then did a dummy workout, consisting of 1 minute. This seemed to force the one that was in the “Waiting to sync” status to sync; in my case, uploading it to Komoot.