Why does Ghostscript show /undefinedfilename when working on files on external/secondary disks after upgrading to Ubuntu 25.10?

I am puzzled by the following issue: When converting an *.eps file to pdf, I used to use the following Ghostscript command (note the file locations are on some secondary hard drive or USB stick)

gs -sDEVICE=pdfwrite -o /media/E6EA-F86E/test.pdf /media/E6EA-F86E/test.eps

which used to work seamlessly up until I upgraded from Ubuntu 24.04 to 25.10. According to the packages list, the Ghostscript version used was 10.05.0 for both distro versions, so nothing inherent to Ghostscript should have changed by this upgrade. Still, I now get the output

GPL Ghostscript 10.05.0 (2025-03-12)
Copyright (C) 2025 Artifex Software, Inc.  All rights reserved.
This software is supplied under the GNU AGPLv3 and comes with NO WARRANTY:
see the file COPYING for details.
GPL Ghostscript 10.05.0: **** Could not open the file /media/E6EA-F86E/test.pdf .
**** Unable to open the initial device, quitting.

Adding -dNOSAFER does not change the outcome.
If I however move the EPS file and the output file destination to my primary system drive (where also Ghostscript is installed to), it will work as usual. If I just decide to keep the source EPS file to the external/secondary drive and the output still on the primary drive, I see more information:

GPL Ghostscript 10.05.0 (2025-03-12)
Copyright (C) 2025 Artifex Software, Inc.  All rights reserved.
This software is supplied under the GNU AGPLv3 and comes with NO WARRANTY:
see the file COPYING for details.
Error: /undefinedfilename in (/media/E6EA-F86E/test.eps)
Operand stack:

Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push
Dictionary stack:
   --dict:747/1123(ro)(G)--   --dict:0/20(G)--   --dict:85/200(L)--
Current allocation mode is local
Last OS error: Permission denied
GPL Ghostscript 10.05.0: Unrecoverable error, exit code 1

However, all files and directories I am working at have full read/write access, running gs with sudo does not change the outcome either. I tried this with both my secondary disk and an external USB drive with the same outcome. And it only started to be a problem after the Ubuntu upgrade. What is going on here?