In model.py function clear() which calls solution.java.clearSolution() is not working for COMSOL 6.2.

See 6.2 COMSOL manual:

From version 5.3a, the method model.sol().clearSolution() is deprecated and replaced by the method
model.sol().clearSolutionData() since clearSolutionData generally works as expected, while clearSolution clears settings unexpectedly.