I think Evans' distribution is suffering notably at the minute for a few reasons:
1) Lack of match fitness/sharpness - Has played very few games in this calender year and has really struggled to get any sort of form going as a result. Fatigue as the game goes on probably resulting in poorer decision making and execution.
2) Lack of confidence - Linked to lack of sharpness, him being worried about this shortcoming being exposed, also previous mistakes this season perhaps playing on his mind.
3) Change of personnel - Hasn't had time to get used to play with new signings like Rojo at the back, or McNair who came in to the side while Evans was out. Communication therefore a problem and also leading to mistakes.
4) The 'Philoshophy' - Onus is on playing out from the back and keeping possession. Evans making more passbacks and putting other centrehalfs in bother where before he might have went long to avoid trouble.
5) Lack of movement - Used to having the likes of Paul Scholes or Carrick showing in midfield, and Patrice Evra racing down the side of him. Now he has the cumbersome Fellaini trying to find space, and the go to man Carrick instead now alongside him.
6) 5-3-2 - Also linked to No.5. Evans is taking up the position a left back would usually occupy when we're playing out and he's finding himself more boxed in. The channel to the left wing back is narrower, and instead of having 2 outlets (you could be certain the marauding Evra would be one) on this side he only has 1, the LWB who's nearly always marked. Infield is often congested with the likes of Fellaini poor at making himself available, and Mata also getting crowded out when on the ball. Decision making we've seen is often slow and sometimes careless.
Certainly he's been poor for the reasons outlined but i'll not be getting on his back until he's had a good run of games in a settled defence, and hopefully a formation more suited to him, with the 5-3-2 doing none of of our defenders any favours at the min.