Just to answer a solution that seems a lot more simple than some answers, and get things clear in case anyone is looking this up as I have been today.
In order to sync pattern changes made manually or in arrangement mode on the Octatrack (OT) when connected to other Elektron gear, the way to do it with MIDI SYNC is as follows.
On your OT, set the following in MIDI SYNC
TRANSP SEND > ON
CLOCK SEND > OFF
PROG CH > SEND > ON
PROG CH > Ch 16
On your Rytm/A4/DT/DN etc, set the following:
May vary slightly, but same principle applies - I am refering to a Rytm MKII menu.
(MIDI CONFIG > SYNC)
CLOCK RECEIVE = OFF
TRANSPORT RECEIVE = ON
PROG CH RECEIVE = ON
(MIDI CONFIG > CHANNELS)
PROG CH IN = CH 16
Often the AUTO channel seems to be set differently by default on various Elektron gear. Also Clock and Transport apparently interfered. Anyway, this is what sorted it for me. Hope that helps!