Update 2020-08-30: SMA published a firmware update that fixed this problem.

Our solar install has shut itself down after detecting an arc fault four times since we installed it eighteen months ago: 2019-03-24, 2019-04-10, 2019-08-17, and 2020-02-17. The 2019-04-10 shutdown was with error code 4301 while the other three were with code 8206. Per the manual for our SunnyBoy 5.0 inverter, these codes are:

4301: The inverter has detected an electric arc. The inverter interrupts grid feed-in and cannot connect to the utility grid.

8206: The inverter has detected an electric arc and was recommissioned after a disconnection.

The inverter can take up to three strings, and ours is configured with two. A sensible inverter would track which of the strings the arc fault had been on, to help narrow down the problem, but apparently this one doesn't. The techs decided to turn off one of the two strings, and see if the fault re-occurs. Based on four faults in 18m, with the longest interval of 6m, you'd need to wait about 8m with no faults before being pretty sure the problem was with the disconnected string. This seems like a long time to be producing at half capacity, but apparently inspecting an installation on a steep roof to locate an arc fault is very difficult? This doesn't make much sense to me, but also I don't know much about it and kind of need to take the techs' word for things.