Problemshooting for shower drain

Underneath existing shower a continuous leak was discovered, resulting in the shower being redone and redoing the waterproofing. Leak test was done before tiling began and passed with flying colors. After tiling, area around drain stays wet, no leaks, just the tile doesn’t dry and white gunks form on top of drain. The inside of the drain was cleaned several times as well. Tile chosen was pebbled rocks with large gaps between each pebble. Any suggestions for why the drain area is not drying and what the white gunk may be?