Sounds like it might be a problem with the Itch client on your machine, which I can't control. I also have the Itch client and when I launched and updated Maelstrom, all the files are there for me.
it is a client problem. Access denied but it only applies to Maelstrom in DirectX_64bit folder. Could you perhaps send me Maelstrom for that in an e-mail? I could then hopefully continue playing until the problem is solved. Or a complete Maelstrom folder.