Open grib file using xarray and cfgrib

Question

Using the xarray and cfgrib can open the grib file with the command ds=xr.open_dataset('a.grib',engine='cfgrib').

However, the dimensions of ds sometimes are different from those obtained from the offical.

For example, the dimension of ds should be [time(31),step(16),lon(2576),lat(1280)], but the result obtained from the xarray and cfgrib is [time(31),step(16),value(1661440)].

Is there any ways to solve this problem? Thanks in advance.