Windows Credentials Disappear

I am working on a network where file sharing requires passwords.  There's a mix of Windows 7, 8.1 and 10 systems.
In order to make this work, we have created Windows Credentials on the "client" computers' User profiles.  These show up in Windows Credentials as Enterprise type.  This seems to be working quite well.

However, I've seen cases where the "client" has had access and now can't gain access and find that they have NO Windows Credentials.  This is the case even though I know the credentials were set up previously on that client computer and user profile.

Just FYI:
In some cases, the access is inter-subnet where there is no inter-subnet name service.  So, naturally, we use IP Addresses.  And, of course, the Windows firewall on the "server" needs to include the client subnet in the file sharing rules scopes.  So this should not be an issue.  Lacking this, inter-subnet file sharing won't work.

Also FYI:
It appears on the local subnet that credentials set up for [computername] do not work for [ipaddress] and vice versa.
So, if the user might access using either method, a credential for [computername] and another credential for [ipaddress] seems necessary.
Of course, for inter-subnet file sharing there can only be [ipaddress].

Because the access policies are rather strict, I need the establishment of the Windows Credentials to be robust.  
I'm wondering if there is some process that might delete them automatically?  Like CCleaner or ..... ?
I'm wondering if there isn't some setting or process that we're missing beyond "remember this..."?

In reading about this, I'm now wondering if the User Windows login password is changed, will that wipe out the Credentials?  What I saw today had that element mixed in.  And, the email pop password also seemed to be gone.