Running the following snippet of python code:

import z3
a = z3.BitVec('a', 5)
b = z3.BitVec('b', 3)
cond = z3.simplify(z3.BV2Int(a) == z3.BV2Int(b))

The simplify call fails with:

z3.z3types.Z3Exception: b'Sorts (_ BitVec 5) and (_ BitVec 3) are incompatible'

possibly because it is trying to unwrap the two BV2Int calls without making sure the underlying BVs are the same length.
This reproduces with the 4.13.1 release (and later). It does not show up in 4.13.0.