I check my agenda, all the .org files are open in buffer, agenda shows up fine
I open some buffers from network share, which then became unavailable out of home
I try to update my agenda
agenda gets empty because those files are not available
but the buffers are available in Emacs
so I suggest to read from buffers if files are already open in buffers instead of insisting files being available
this is my setup:
(setq org-agenda-skip-unavailable-files t)