wave speed exceeds 1 in an eulerian element(CEL simulation)

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wave speed exceeds 1 in an eulerian element(CEL simulation)

I am running a CEL simulation in abaqus.
It is a kind of oil damper. The oil goes through small gap to decrease the
speed of piston.  Most part of the fluid speed near the gap is about 2-10
m/s, which is right. However, part of fluid speed before the gap suddenly
becomes very high, near 1E+11 m/s.And then two ERROR appear, which are shown
as follows.

***ERROR: The ratio of deformation speed to wave speed exceeds 1.0000 in at
          least one element. This usually indicates an error with the model
          definition. Additional diagnostic information may be found in the
          message file.

***ERROR: The fatal error will generate a new field output in the last
          increment. All variables applicable to the current procedure and
          material type(s) will be written to the output database

I think my ERROR may be related to the element distortions. Because I find
that my Eulerian elements has some deformation, which should be fixed in CEL
simulation. As shown in the pictures, the element in the green circle have
obvious deformation under the "Deformation Scale Factor is 1". This really
confuses me. And the ERROR elements are in these elements, whose wave speed
exceed 1.

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