If it is a bug in the software, check to see if others are having it (on the Cubase site, somebody will be complaining if there is a bug). No need to chase something you can't fix. Seems like you are doing this, but just to confirm.
(Assuming Win-X)Otherwise, you have most likely something wrong with your Audio Interface or its drivers. Defrag will not help, that would help with I/O
performance, but not this issue. But you could check hard disk integrity as it could possibly have a bad spot(s), (use the check drives for errors under tools) bad sectors could corrupt drivers/software/OS and cause an error.
Last, you could have either have a bad hardware unit (it happens that some part of the manufacturing process had a flaw and you hit the flaw at some point in the process and causes an error/crash), or your drivers could be corrupt (try removing them as completely as possible, reinstall), look for an update, etc. to the interface drivers. Swap USB ports, just to check.
Lastly, and not very likely, you could have a bad RAM memory. If there is a flaw in it, you could hit a bad area causing the issue. Also, CPU could have an issue, but these last two things are getting to be so rare, I rarely check for these days and just has a low probability, but it could happen. (This would be a last resort kind of thing)