Welcome to the forum!
I can't say whether those gaps represent a bug or wrong behavior, since I don't know the exact steps you take in the file. Just with some brief testing, I cannot reproduce it.
If you'd like to investigate the gap, would you please provide the SVG file, and if possible, with some typical objects which you apply Fractalize to. If you can reproduce it, please undo the step which creates the gap, save the file, and share it with us. Then tell us how to reproduce it.
If you don't want to investigate the gap problem, but just know how to fix it -- you won't be able to add a node where there isn't already a path. What you need to do, is select the path with the Node tool. Then you can see the existing nodes. After that, there are a few options you could use.
You could use some buttons on the Node tool control bar (the bar of icons just above the horizontal ruler). First, select the 2 end nodes. Then click either "Join selected nodes" button ( 
) or "Join selected end nodes with a new segment" ( 
). Either of those 2 will close the path, and then you try Fractalize extension again, or just add extra nodes to the path.
Or you could swith to the Pen/Bezier tool, after the path is selected. Notice the tiny square at the beginning and end of the path (at the end nodes). Position your mouse inside one of those squares and click once. That will start to extend that path. Click once whenever you want to place a new node. And click inside the other tiny square, to close and end the path.
Hey!
I can easily recreate the issue in a new document:
Step by step how I put this file together;
1. Create new layer named "Water" (delete original layer.)
2. Add a rectangle shape with
to the "Water" layer.
3. Create new layer named "Land".
4. Add object using
to the "Land" layer.
5. Duplicate the object made with
and place it on the left (to show original shape)
6. Apply Fractalize on the island to the right.
7. Create "Text" layer and add text for reference, using
Using
on the fractalized object where the issue appeared, fixed it partially. However using fractalize again on the object produces the same issue.
I've applied fractalize on shapes ranging from simple 5-7 node objects, to larger objects with 1000-2000 nodes, they all come out glitched in at least 1 area.
Since you can't replicate the issue my guess is that my installation went wrong, in that case I'll reinstall and report back.
I'll attach the .SVG to this post.
edit; I reinstalled the program and got version 0.92.3, now the Fractalize extension won't work at all. I try applying the extension on an object but it remains the same
