Every so often I'll get an ATC message where ATC is directing one of the AI's (usually A320) to 'please expedite climb to FL XXX" The message repeats often until I go out of that frequency range. I can't tell if it's the plane that isn't responding or it it's an erroneous transmission. I can't tell what altitude the given plane is at. Anyone else run into this?

Usually the flight plans have been written with a cruise altitude too high for the flight dynamics of the aircraft.What flight level was the last one?This is opposed to the new generated AI aircraft which must find the correct flight level just after it is created. Those usually only take one or maybe two calls before they are on course.

it was FL 310 for an Air France A320. Shouldn't be too high for that aircraft, I wouldn't think.

Some of the older AI flight models exhibited this behaviour. Most, if not all, of them have since been corrected. Check the model version that you have for the affected AC.