unscheduled calibration ???

My system decided to dump all battery charge to the grid in the middle of the charge window at night so when I got up in the morning it was charging at expensive rate. I restarted the inverter and that stopped the charge for a couple of minutes and then it started charging again. I turned AC charging to OFF but that made no difference. I managed to stop it by changing the battery charge power to 0.
It almost looks like a unscheduled calibration since the battery was discharged to 0% and ignored the 4% reserve.
I am running on BMS 3013 (that was installed and run full calibration in August) and Gen1 HY 5K inverter.
Any ideas is going on?

Without seeing the battery soc graph, it's difficult to say. My guess is the state of charge was inaccurate and dropped suddenly to zero from a figure above 4%. The battery will then automatically charge back up from the grid to the 4% reserve.

Sure but none of that happened. Battery discharged at full power to the grid for about 2 hours then started charging at full power (and still is charging).
Battery is and was on Eco.

It does sound like a full calibration. Either accidentally kicked off by support (unlikely at that hour), or a misunderstood/corrupted modbus command, or a software update happened that needed a calibration after.

Probably a question to ask GivEnergy over email or web chat via their website.

I've had this happen 3 times, feedback was GivTCP can write to incorrect registers, only later versions of firmware and GivTCP add verification checks to erroneous writes. Inverter reports in eco, discharge schedule is passed and discharge is off, yet it dumps to 0 then performs a grid charge to 100.

For two of three Giv support were able to cancel the "top end calibration" the third I let run.

I had the same thing early hours of Thursday morning