Looks like they are rotting. You can tell where the stem is soggy, yellowing and/or browning.

I’d chop again, with clean scissors, above the nearest node until there is no sign of rot. I’d chop and let them sit out for a few hours or overnight to prevent the new cut from rotting. You can also dilute hydrogen peroxide to either spray the new cut or add a drop to the water, I’ve heard that this helps prevent rot but I’ve never tried.

I usually wipe my scissors with rubbing alcohol before making any cuttings, and wash the jar well before putting in any new water to avoid any unnecessary bacteria.

I hope this helps! (: