Running out of memory in custom dimension

Whenever I enter the custom dimension I've created the memory useage quickly increases till the game crashes stating it ran out of memory. Replacing either the barriers or end portals with stone solves the issue. Anyone know what's happening here? The dimension code is below:
{
   "type": "kelraw_ddm:inner_sea",
   "generator": {
      "type": "flat",
      "settings": {
         "biome": "kelraw_ddm:inner_sea",
         "layers": [
            {
               "block": "air",
               "height": 16
            },
            {
               "block": "end_portal",
               "height": 1
            },
            {
               "block": "barrier",
               "height": 1
            },
            {
               "block": "water",
               "height": 1
            },
            {
               "block": "barrier",
               "height": 1
            },
            {
               "block": "water",
               "height": 1
            },
            {
               "block": "air",
               "height": 60
            },
            {
               "block": "barrier",
               "height": 1
            },
            {
               "block": "water",
               "height": 1
            },
            {
               "block": "end_portal",
               "height": 1
            }
         ],
         "structure_overrides": []
      }
   }
}