@SmartGirl 

Don't know the answer for the specific router, but I've got no problem on my A20.

I'm on W10, and I have a Windows Credential that supplies the UserID and Password needed to access the drive:

At least I recall that worked. I don't do that anymore so I can't be sure (use Access Autorization) as my DLNA client can't handle the access request. I don't share it over the WAN either.

I suspect you had created that Credential for the old router and forgot that is how it was done?

I could be wrong, but doing the above might work for you now?

@IrvSp I'm not sure how setting some values on 1 of our 5 internal LAN machines would cause:

Every inside the network to NEVER need a password, but can still read+write. 

But someone 1000 miles away *WOULD* need a read-password.  And be forbidden from ever writing.

I'm pretty sure 100% of this was done INSIDE my old router, where the thumb drive lives.

SmartGirl wrote

@IrvSp I'm not sure how setting some values on 1 of our 5 internal LAN machines would cause:

 

@SmartGirl 

Correct, that would need to be done on every PC, not just one.

Unless you knew what you set  on the unspecified router, I can't think of anything, unless it had some 'access control' setting for LAN devices? Of the router's I've used, LinkSys, ASUS, Netgear, and TP-Link.

All I've used required a UID and P/W by the device that tried to use the USB drive when it was protected.