CRS326-24S+2Q+ MLAG issues

Hello,

I have 2 x CRS326-24S+2Q+ running v7.16.3 and 7.19.2. To port 8 of each of these switches, I’ve got a S-RJ01 that’s going to a Synology NAS. Port 14 and 15 of each switch connects to the other switch, and a bond 802.3ad is formed over those ports. I wanted to give MLAG a try, but I seem to fail, for some reason.
Here’s what I did:
Enable MLAG from the bridge, using the inter-switch bond as the peer interface. MLAG status seems fine, one’s a primary, one’s a secondary.
Cteate a bond 802.3ad on each switch with the same MLAG ID, with a single slave - port 8 - going to the Synology NAS.
On the Synology, I created an 802.3ad bond.

Everything seems to be online, but I can’t get traffic through the bond at times. At other times, the traffic works, but testing from multiple sources still yields just 1 Gbps.

Does anyone have any tips for getting this running?