Swift flood fill algorithm randomly stopping

Question

Here is the raw code but I will explain it roughly:

func processTile(_ tile: Tile) {
    // Add tile to pos list if valid, otherwise prune the 
    branch
    if isBarrier(tile) || alreadyChecked(tile) { 
        return 
    } else { 
        posList.append(tile.pos) 
    }

    depth++ ; if depth > maxDepth { return }
    
    for neighborTile in neighbors(of: tilePos) {
        processTile(neighborTile)
    }
}

This is the main recursive function. Basically it checks if a tile is part of a room by being neither a barrier tile or already checked. If either one of those cases is true then the branch of the flood tree is pruned and ended. If the tile was valid and was added to the list then the depth is incremented with a check on it. Then the tile's neighbors are all checked with the same process.

For some reason the flood algorithm just stops randomly. I changed the code adding a print() in front of the returns to see why a branch just stops. This worked for all the correct pruning cases where it hits a barrier or already checked tile, but when it would just randomly stop and not check a tile it didn't even log anything.

The only thing I can think of is that Swift stops executing the functions after a certain level of recursion. If this is the case does anyone know what the maximum number of recursions is? And what a possible workaround would be. I'm thinking you would have to make a list of all the "edge" tiles of the flood, and a list of all the "interior" tiles of the flood. Then have a while loop running until there are no edge tiles which just expands the flood.