Your cell data is written every 1 second while the particle data is written every 0.01 second. At time=0.21s, there is no cell data to display besides the initial values, this is why you see a uniform field. Change the write interval for the cell data to 0.01s. Otherwise you have to wait until the simulation reaches 1 second to see new values.
I suggest you update to the latest version of MFiX (23.2), it has better controls for the visualization than 21.4.