When opening vim with -d (diff) mode, two windows appear in a diff-fashion (e.g. marked lines etc.). When saving and opening such a session, the result is the same two windows, without the diff.
Reproduce:
create two files a.txt and b.txt
vim -d a.txt b.txt
:SaveSession diff (you can see the diffs marked)
:OpenSession diff (you cannot see the diffs marked)
When opening vim with -d (diff) mode, two windows appear in a diff-fashion (e.g. marked lines etc.). When saving and opening such a session, the result is the same two windows, without the diff.
Reproduce: