It sounds like you created two separate sync chains. They can’t each have their own. You create a sync chain for one and then on the other you have to add it to an existing. For example, did you do as I shared at Helpful Info & FAQ for Brave Users - #38 by Saoiray for either device? Where you scanned the QR code or entered some words?
So one of them would have a sync chain created and you would then use it to generate the code that your other device would use. Let’s pretend you do that on your Desktop. So then on your tablet you would go into Sync and choose to join an existing sync. It would ask you to scan a QR code or enter a sync phrase. You would do that using the code or phrase generated from your computer.
Once that is done, you should see both devices listed on the sync chain together.
Since you don’t currently see both listed on the same sync chain, you will have to Delete Sync Chain on one of your devices so it can then join the one your other device is on.