The difference could be due to small changes that happen in algorithm over versions. To get to the root of the issue, make sure that you are using the same mesh that you used in the older version (This can be done by opening the old saved project with results and then clearing the results and rerunning them in the newer version), and use the same number of cores and then check the difference in results.
When we have physical or numerical instability, this type of behavior is expected. We document this in the following locations:
Please check the last paragraph for both pages. This sort of behavior is most commonly seen in nonlinear static or transient analyses which are numerically unstable and using different cores to solve can give slightly different results.