Want to go over the physical changes required to convert a Split-Phase XW Pro to Single-Phase in preparation for 3-Phase mode.
Internally:
On upper connector, X2 moves from Neutral to L2 and a Jumper is placed across Neutral and L2.
On lower connector, X3 moves from Neutral to L1.
AC Connectors:
Jumpers between Neutral and L2 are installed for Load, AC1, and AC2.
Neutral to PDP Neutral busbar is attached to AC1 Neutral
The AC Sync RJ-45 connectors are using to chain all three inverters together with ethernet cables. (No terminators)
Xanbus RJ-45 connectors chain together with ethernet cables. The first and last device on Xanbus require terminators to be installed in the open port, with the exception of internally-terminated devices like Insight Home.
Once that's done the XW Pros can be energized in standby and configured to 3-Phase Mode Primary/Secondary/Secondary in each the three inverters.
Since you said you had it running I could presume all that was handled, but double-checking those changes and jumpers would be where I started if I was fixing it.