@maxpolzin 18 FPS when using ULTRA depth mode with Xavier NX is expected, you can start ZED Depth Viewer with the same settings to confirm it (look at the FPS reported in the bottom left corner).
You can use PERFORMANCE to increase the FPS if you need.
I noticed that your camera has an old MCU FW Version, I suggest you use ZED Explorer to upgrade to the latest v3.10 (778) and obtain more reliable camera connections.