Hello,
Are you using the Legacy driver just for keeping the .mpp file? The new driver should also retain the .mpp in your Documents folder. You can also choose to retain both the .mpp and the .xml by changing the file under Documents\logs\logger.properties "general=debug". We recommend using the new driver instead of the legacy driver.
There are several things that could be happening here, I will mention a few to review and if none of them help, I encourage you to open a Support case.
The first is that the Legacy driver requirements for MSP are that only MSP 2013 is supported. That means, no other patch should be installed, including SP1 or any monthly patch that MS is releasing.
The new driver on 15.1 supports either MSP 2013 SP1 or MSP 2016, as long as they have at least February 2016 patch installed. The list of supported patches (new driver, v14.4 and later only) is mantained here: http://www.ca.com/us/services-support/ca-support/ca-support-online/knowledge-base-articles.tec1830355.html
The second thing is that it might be related to an existing defect that might have already been fixed. Try with the latest PPM patch (and remember to re-install the integration) when possible.
If after reviewing the above the issue is still happening, please open a new support case with as most detail as possible on the Steps to Reproduce, versions you are using and other details that you might have so that we can help you.