Keep in mind that these type of cameras, although are spec'd and capable of these various parameters, real world testing by many of us shows if you try to run these cameras at higher fps and higher bitrates than needed that you will max out the CPU in the camera and then the camera bugs out just long enough that you miss something or video is choppy. My car is rated for 6,000RPM redline, but I am not gonna run it in 3rd gear on the highway at 6,000RPM...same with these types of cameras - gotta keep them under rated capacity. Some may do better than others, but you are running the CPU higher.
Look at all the threads where people came here with a jitter in the video or IVS missing motion or the SD card doesn't overwrite or gets an error in BI and they were running 30FPS and when people tell them to drop the FPS and they dropped the FPS to 15FPS the camera became stable. As always, YMMV...
Movies on the big screen are shot at 24FPS, I do not think we need 30FPS for our mobile devices and tablets LOL. Shutter speed to capture details is much more important than FPS.
15 FPS is sufficient for surveillance cameras.
And is your camera going thru a router? That can cause it as well as they are not designed to deal with the data demands on these types of cameras.
You also mention the FPS is jumping around in BI - that is usually a power issue with the camera.
TL

R - Drop the FPS and iframes to 15; make sure you are not going thru a router; and check the power on the camera - is it getting enough - test it all by itself on a POE switch and see if it goes away.
If it is still there after, then in BI redo the find/inspect and up the bugger at the bottom of that screen to 20.