Not able to access external drives via SMB on Mac OS Catalina

Since upgrading to latest security update on Catalina, I am unable to access external drives attached to my Mac Mini, from my MBP via wifi. There must be a new permission I'm missing, but can't work out what it is. Sharing from the Mini is active, and I can access files on the mini, but not on the network. Not sure what to do next.

Before you ask...

1. SMB and AFP access are turned on both machines.
2. The MBP is running Mojave and the Mac Mini si Running Catalina 10.15.7 with the latest security update.
3. I am able to access hard drives on Mac Mini via SMB, but not the attached external drives.
4. My external drives are shared as share points on the Mini and can be seen from the MBP. However, as soon as I try accessing them, I am getting an error saying I do not have the permission to access the server or that the "item could not be found" (this error is especially a weird one).
5. I am able to access the external drive locally (on the Mac Mini).
6. Both machines are on the same wifi network.
7. I tried toggling the file server on both machines and, as I said, I am able to access the contents of the hard drive but not the external one.
8. Since this is a mac Mini 2012 machine, I do not have the option of upgrading, unfortunately.
9. I toggled all the advanced options (right-click on the share point name under System Preferences -> sharing) and ensured that the "time machine access" and "SMB access" are allowed for the external drive.
10. I even tried other external drives and the exact same issue happens with them.

Is there anyone else here who has encountered a similar issue and figured out how to solve it?

Alternatively, might you have some ideas that I could try?

Thanks!