70 Hz, that's from SI?
That's higher than I thought it would go, and only goes high when being backfed e.g. by GT PV.
Separate to simplest setup.
SI & batteries, ground wire connected to house ground, AC2 input from grid shut off. AC1 output going to loads only (no Sunny Boys), not wired through any transfer switches.
Start that up, check voltages between L1, L2, N, G and check frequency.
Try powering loads with no GFCI. Then powering loads with GFCI. Then feeding grid to AC2.