I have been getting this with one on my ML2 a lot lately:
[2019-01-06 09:09:30] FutureBit Write error: Input/output error
It will work after being re-plugged in but only for a day or so.
Anyone have any clues as to what is causing this?
That means device dropped out completely from hub/USB port, and it will not reconnect on it's own, you need to unplug it to have it back.
I would try different USB hub / different USB cable.
Maybe not your same problem but I am running 2 moonlanders off a 4 port hub for a year now with a 8A PSU. Recently started getting the same thing. Turned out the contacts in the hubs USB ports got "tarnished" or something. Possibly due to the high amp draw and the cheap port contacts used in it. A simple bump to the desk or cords would cause enough vibration to cause the same thing to happen. My hub runs pretty hot right at the ports too... The moonlanders seem to transfer some heat to the ports or due to amperage they just get hot.
Anyway I cleaned up the contacts on both the ports and the moonlanders. In the hub ports I used a X-acto knife to bend the contacts up (they flattened over time again possibly due to the heat) so when plugging back in the moonlanders made solid contact. Problem solved.....
Hope that helps,
Bob