If you are missing keyframes at the end of your animation in an exported FBX file, they may have been cleaned by the 3ds Max FBX plug-in Constant Key Reducer filter. When this filter is enabled, the plug-in removes any consecutive keys that have the same value.
For example, if you set five consecutive keys of the same value at frame 10, 12, 15, 20, and 24, the constant key reducer filter will remove all the redundant keys except the one at frame 10.
During import, the plug-in may resample some animation curves. If this resampling occurs, the 3ds Max FBX plug-in automatically applies the Constant Key Reducer filter to reduce the amount of keys allocated in memory.