The first time I ever did candles, I used untreated wicks, which caused this ghastly indentation around my wick. Did several repours and it just ate up more, because the wick was untreated.
Use a wick that's been dipped in wax. The raw wicks, the ones that don't have wax on them will suck up wax and cause a sink hole around it.
You can cut and pre treat your raw wicks with plain melted wax, which will solve the issue.
You can tell if your wicks are pre waxed or not by feeling them. Do they feel waxy? Are they stiff? Is there a coating on the wicks? Then yes, the wicks are ready to go.
Is your wick material like braided thread, floppy, soft and easy to manipulate around your finger? When you scratch the wick are you just causing the threads to tangle and or come undone? Then you need to treat your wick material with wax.