Hopefully your consumption in the home during the day is used from solar, that's where the bulk of solar savings are made.
I have heard of wiring done wrong, where solar feed is added to usage on a meter, but usually it's a permanent thing (and found very quickly on post install checks), not something spasmodic as you describe.
Strangely, it could well be a rare meter issue.
Where are you seeing this, on the AGL account usage info, daily view chart ?
Your solar has an app and shows the real picture ?
