Consider increasing your forum trust level to basic user (https://forum.qorvo.com/t/qspice-forum-new-user-to-basic-user-file-upload/24340), which will allow you to upload your .qsch and C++ code if you need a more detailed review. Alternatively, you can review what the .tran waveform looks like. In general, you can usually figure out why the system is struggling to get a smooth Bode plot by looking into the input and output signals for that specific frequency duration. Instead of using my FRA, you can also consider .bode command in Qspice.