Confused by this (read/write, but not delete access?)

Recently I've been having issues saying "I don't have permission", and, it's only for deleting items. I can modify/add items fine:-

The reason why I'm so confused is that only "Nicholas" is allowed to have read access, I only have three users on my unraid box (that have SMB access), all three of which have a password:-

Root

(Personal account name)

Nicholas

My unraid user/pass for "Nicholas" is the same as my windows user/pass for "Nicholas" (And thus it has never asked me for my unraid user/pass):-

And here's the settings of the share:-

So, my question is:-

How do I have permission to read/write but not to delete?

EDIT:- Fixed it by running the below in terminal, but, my question is how did the files lose my permission? I placed them there, shouldn't I instantly have the ability to delete them? I made them after all.

newperms "/mnt/user/Nicks files"

I don't want it to happen in the future, why I'm asking the above (in bold).