This issue was introduced in f3423b8a773, which assumed that number of input channels matches the number of outputs. With flexible I/O this is not necessarily the case.
This fixes #9106, along with the previous commit.
82512422a7 Deliveries support mismatched chan-counts
libs/ardour/delivery.cc | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)