Placeholder nodes overwrite nodes inside the graph and don't revert back

Steps to reproduce:

1. Create a graph with custom nodes.

2. Delete the custom nodes back cs files. Wait for domain reload

3. Reopen the graph, see the nodes have been replaced with placeholder nodes

4. Bring back the cs files for the nodes.

Actual results: 

Graph still contains Placeholder nodes.

Expected results: 

Placeholder nodes should revert back to the original nodes

Reproducible with versions: 1.0.6

Not reproducible with versions: 

Can’t test with versions: 

Tested on (OS): 

Notes:

• This can also happen due to bad domain reload that fails to load the nodes correctly.