Surely it cannot be RAM issue if file copied directly from second PC to Unraid matches md5?
All the mis matches are coming when my windows PC is involved, as both my Unraid server and my second PC are accessed via SMB so all the testing apart from the last test has been via my windows PC. By that I mean, when I copied file from second PC to unraid the first time round I used my windows PC to do that. While the second time I did not use my windows machine and did it directly from second PC.