I know this is an old thread, and that you may have fixed the problem or given up altogether, but you should be able to fix it using Task Manager (speaking from personal experience). First, get a task manager priority locker like Prio, Process Lasso, or Process Hacker (I suggest Prio, much simpler and easier to install than the others, find it at https://www.prnwatch.com/prio/). Then, after installation, open FBX. Open Task Manager as well. Navigate to the details tab and find the process labelled BBPlayFx.exe. Right click, make sure "Save Priority" is checked, then set the priority to High or Realtime. By default, it is set as normal. This allots slightly more system resources to the application, allowing for less or no frame drops in the recording.