TL;DR: Seems to be a BUG 
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I’ve only had the SG briefly so not exactly experienced with it (so there could easily be something I’m missing) but I’ve been through the entire manual, and I’ve just done about 2hrs of testing this and there does seem to be a bug with the Arp timing, from what I can see.
My SG is on the latest firmware v1.26
I have it clocked to an Elektron Octatrack (over 5-PIN MIDI, no USB cable connected).
The Octatrack has been absolutely solid as my master clock for all my gear for years. Never had a single timing issue.
I had a drum loop going on the Octa so it was very obvious when the Arps weren’t in time. I haven’t tried another clock source yet but it’s very unlikely the Octatrack has anything to do with the issue.
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SYNC SETTINGS (SHIFT > SYNC [EXT CLK]):
Button 1 - Clock Transmit is OFF (flashing #1 LED)
Button 2 - Clock Receive is ON (solid #2 LED)
Button 4 - MIDI Stop Message Receive is OFF (flashing #4 LED)
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The Tempo LED blinks in time with the Octatrack as it should. Changing the tempo on the Octatrack changes the tempo on the SG, and the arps speed up and slow down. They are definitely synced ok.
- I did Shift+INIT PATCH on both layers
- I cleared the Mod Assign on both just in case.
- I manually set all faders, knobs switches to the same (I manually moved everything away and then back to the position I wanted - basically everything off, nothing free running, filters fully open without res, no LFOs, no binaural, no pw/drift/spread/phase, no portamento, no dynamics, no effects etc etc.
- Arp set to 1/16 on both
- SYNC (button in the Arp section) ON for both layers
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Going between SINGLE and DUAL modes, (and in each mode, testing between LAYERS), the arp timing is completely inconsistent, mostly not starting immediately when a key or chord is pressed.
I am pressing the keys in time with the beat.
I thought I was getting somewhere for a few minutes - it seemed like if you change from SINGLE to DUAL mode and disable and reenable each layers’ Arp before pressing keys, they seemed to sync but this proved inconsistent. Both arps were kicking in at different, seemingly random times when keys were pressed.
It also seemed at times that, when in SINGLE mode, if you change layer, but wait for a few seconds before pressing a key, the two arps would be in time with each other, starting at the correct time, but it turned out that when the layer is changed once or twice, it loses timing again. Most of the time the LOWER layer was ok and in time with the beat, while the UPPER layer was way out of sync and not starting for some milleseconds - up to about half a second.
No apparent consistency with the Arp start. I didn’t take video but it’s quite easy to reproduce. Same after power cycle. Same with any other settings (switch/button positions) I tried. Stopping and starting and power cycling the Octatrack made no difference to the issue. Powering on one or the other first made no difference.
Same results trying DDS 1 on both layers (DDS2 turned down), versus DDS2 on both layers (DDS1 turned down)
Don’t know if I’ve forgotten anything there.
I plan to raise a ticket with UDO Support myself about it - if it is a bug, they may well be aware of it already and working on a fix, I’ve no idea but it definitely seems to be a bug.