I am not an AWS/OntapCloud guy, but just made some observations from the image you have shared:
1) Looks like Sync is in progress (Scanning phase) - So it is probably still processing the directories/files and not finished yet. That could explain no data is seen yet.
2) After the scanning is done, and the differences are calculated, DataSync transitions to the TRANSFERRING status. At this point, DataSync starts transferring files from the source file system to the destination. Only files that have been added, modified, or deleted are transferred.
Could be that the data is constantly being changed on the folders that you're syncing which keeps CPU high until all files have been synced, and probably the CPU (instance type with burstable CPU performance)is allowed to burst to 100% when its @peak but should be temperory.
Could you please let us know if it still show 'empty' folder when sysn is done 100%. It would be a good learning for me.