That issue appears to be confined to certain users, and certain outlets, without any real consistency to enable a definitive cause. Most users report no problems whatsoever, while a select few have a serious injector/port fouling problem.
First off, this is 100% E85, and US E85 until the recent ban, used the ether additive MTBE as opposed to AU production and MMT. I'd suggest that considering the widespread use of E in the US and EU, there's little evidence of this problem generally occuring, and I'd be inclined to think it's more from a heavily contaminated fuel tank and components, stale degraded fuel, electrolysis or some similar cause.
It certainly doesn't apply to splash blends of E, as the accepted remedy seems to be to run a couple of tankfulls of ULP, in most cases it's encountered.
It may even be the result of phase shift in the fuel tank as a result of water contamination. It seems that levels as low as .5% water contamination can cause phase shift and resultant layering, and this can compound itself by continually topping up the tank, rather than draining and flushing with ULP.
There's also reports of the possibility of some stations storing E85 in tanks where previously ULP and diesel were stored, leaving a black sludge residue on the bottom of the storage tank, and naturally disolved into solution by the E85..then drops out of solution at the injector nozzle.
A more concerning aspect where US fuel is concerned is the addition of 15% ULP+ in winter grade E85. I understand the additional ULP is only 60 RON, probably as a result of cold weather additives, and how that would impact an average tune. dropped to ~97/98 RON. You'd have to run dual tunes basically.