Animation going to base pose between keys after export

Hi guys first off i am new to animation and blender in general so if i word things wrong i am sorry.

I am trying to make some simple animations. Idle, walk etc… I am also using a third party plugin which i know is not going to be supported here but id like to know whether it is this plugin causing this problem or me.

basically when i export an animation and play it inside game engine it will play the pose i keyframed and whilst blending to the next pose it will blend to the base A pose first . This seems to occur randomly at random times in different animations.

i create a pose, select all bones and insert a keyframe. i then skip a few frames, create another pose, select all bones and insert a keyframe. I then export this to a game engine (using the plugin mr mannequin tools)

some animations i create work fine in the engine, most do what i have written above. I really don’t know what i am doing wrong if i am doing anything wrong, or is it the plugin?

ticking the force start/end keyframes makes some animations work, others not. Its really confusing me.

Any help would be greatly appreciated.