The `matrix_need_update` variable needs to be reset to `false` in
`transfer_matrix_values()`, otherwise that function continues to be
invoked for every scanning loop (forever with `sym_eager_pk` and
`sym_eager_pk`, or until some key gets released with
`asym_eager_defer_pk`), and the scanning rate gets much lower because of
all that useless work.
Co-authored-by: Sergey Vlasov <sigprof@gmail.com>
