There's no harm, but it's not going to do any good.
Each time you try to open the old catalogue, the one that LrMobile knows is the one that you are syncing, you are creating another one with -2 on the end. You are also creating another one which LrMobile thinks may be a backup or copy. So don't open the old catalogue again, and open the catalogue that is the one you want to use, going forward.
If you restart and enable sync, do you get the same message?