It would likely help if you posted the strace output including the lines before and after the "unfinished" system call so that more information is available. The strace output can be so voluminous, it's hard to know just how much to reproduce so that the viewer can draw useful conclusions. That's a matter of judgement.
The "unfinished" system call could mean a number of things, primary among them that the code in the program making the system call has not provided the variables or their values the program is dealing with which are needed to complete the system call.
The use of strace is basically the next best approach to debugging if one doesn't have the source code of the calling program because strace will record all of the steps the calling program makes of the system.