My 10 kw infini showing input islanding in event log...............the problem is that grid relay is connected and disconnected continously at all mode.g  off grid , grid tied with backup.

load is shifted on solar than grid in a repetative manner.....is it software or hardware fault

Assuming the inverter supports all the required anti-islanding signals (I think it does, since it complies with the Australian and South African standards), it means one of three things:

1. Vector shift detected on the voltage waveform.

2. Frequency changed more than allowed in too short a time (ROCOF, rate of change of frequency)

3. Frequency or voltage drifted out of the allowed range.

If it's voltage or frequency, sometimes you can adjust the allowed range (there are guys here on the forum that knows how). If it's Vector shift or ROCOF... then it's an actual islanding event (ie, somewhere on the grid things changed enough to cause a noticeable disturbance) and there would be little you can do about it. I know on some inverters you can set the allowed numbers, but it is rather a technical topic.

This probably won't help you fix it... but let me expand a bit on vector shift. If you think of an alternator driven by an internal combustion engine: When a large load starts, the engine will slow down for a second before it speeds up again. Similarly, when a large load switches off, the engine will speed up for a moment before the governor slows it down again. If you watch it on an oscilloscope, what you'll see is that there appears a little squiggle in the waveform and it passes through the zero line sooner than it should have (on overspeed), or later than it should have (on engine underspeed). This bit by which it misses the proper zero-passing point is known as vector shift.

Similarly, while the engine picks up the load, the frequency will drop for a bit before it goes back to 50, and similarly when the load is switched off: The frequency will spike up and then drift down to 50.

In other words, these vector shift and frequency events indicate something bad happened, so the inverter disconnects for safety.

It turns out that big power stations behave more or less the same way, and even a big iron transformer will show some of that when the grid goes out. So these signals are pretty good signs that you have a grid outage and the inverter should disconnect for safety.