victronics

That sounds like the bus soft start circuit (basically a power supply) isn't turning off. 
Referring to the partial schematic trace (for an Axpert MKS, but may well be very similar), check for 5.2 V at pin 8 of U16, and check R250 and U17. Try a replacement control board if possible, otherwise trace back the connections to pins 1 and 2 of U17 (opto) back to the control board, probably through a buffer chip on the control board. But if pin 2 of U16 is going high (about 5.2 V) when the bus voltage reaches 350-400 V, then that's fine.
I can't think of much else that could cause the bus voltage to rise before the best soft start process is over. Actually, my reading of the bus soft start function is that it doesn't care how high the bus voltage goes, as long as the value it reads is more than a value that depends on the battery and mains voltages. Always between 280 V (for a 40 V battery) and 462 V (for a 66 V battery). So maybe it's misreading either of those? You may be able to check what it's seeing on the LC Display before the inverter shuts off. If both of these agree reasonably closely with a multimeter, then it has to be misreading the bus voltage. Check the resistive divider that cuts the bus voltage down to a measurable value; it likely has a string of high value (say 499 kΩ) resistors all in series. One of these may have gone open or not be soldered correctly.

Unfortunately, it usually means shorted IGBTs, either in the 230V inverter, or the high-side of the DC-DC converter. 
It"s a Bus Soft Start error. There is a small power supply that charges the DC bus capacitors to about 8x the battery voltage (some 400 V), which is switched on very soon after powering on. If there are no paralleled machines, it has about 15 seconds to reach that voltage, or a bus soft start is asserted. A friend and I had one recently (after a repair), and the first time it took about a minute before it came up. Probably the IGBTs were OK at that point. Next startup, the error came up quickly, possibly in just over 15 seconds. There was a dead short across the DC bus. 
It's possible to check this with a multimeter without removing the main board, but it's tricky on some models. Measure on a voltage range first in case there isn't a short. The 2x 470 uF capacitors can hold a wallop, so care is advised. If no voltage, it's safe to measure on ohms. A working inverter should measure in the megohms, slowly changing. 

One big problem is that no-one seems to have a schematic. Well, I've seen a tiny portion of one, so they must exist, but not for the general public.
Apart from getting the bootloader into the processor, there isn't much on the control board that seems particularly tricky, just buffers, op-amps, the power supplies for the processor, and the EEPROM chip. But the back of it is covered in SMD Rs and Cs, so without a schematic, it would be really hard going repairing it.

Oh, it can be done, if you have the skillz. 🕵️‍♂️

Any code 9 errors? @victronics

@plonkster it's the control board that the Axpert and clone PIP inverters is using. @victronics what sort of problems or errors do the invert show when the control board give problems? Where is your repair place based?
 

I don't recognise the control board, what inverter is that from?
In general the answer is likely NO. Because that chip in the middle with the 00010 on it, that is a microcontroller with some kind of programming that is programmed into it, and unless you are very lucky (and the inverter maker is very sloppy) and you have the tools to read it, you can't replace that chip. Well, you can replace the chip, but you can't reprogram it. Therefore, you almost always have to get a new one from the manufacturer, and they will sell you the whole board and not just the chip.