From our DISC science support staff:
I can get V50M in the subsetted file by repeating the selections you listed, i.e.,
Dataset: MERRA-2 inst1_2d_asm_Nx: 2d,1-Hourly,Instantaneous,Single-Level,Assimilation,Single-Level Diagnostics V5.12.4
Download Method: Get File Subsets using the GES DISC Subsetter
Date Range: 2021-02-28 to 2022-05-31
Region: 2.5, 49.5, 3.75, 50.5 (Search and Crop)
T10M = 10-meter air temperature
U50M = eastward wind at 50 meters
V50M = northward wind at 50 meters
I am not quite sure what you meant by "V50M is missing". For my case (Mac machine, Chrome), I got V50M in the files. Please see the attached NASA Panoply screenshot for the metadata and the plot of V50m on the day of 20210228 (one of the downloaded files). As a matter of fact, the selected region is quite small covering only 9 grids with lat=3 and lon=3, thus the plot might look like all missing values. However, if you check carefully the min and max of V50m on the bottom of the plot, you will see that they are not missing.
In order to better assist you, could you provide more information (e.g., machine and browser) and screenshot your results?
In case you are try to get the time series at a point location or over a small region, I would like to recommend other tools to subset and download the data, please refer to this FAQ:
* How do I obtain a time series for MERRA-2 data?