I cant help you directly,...
You can try to install blender 2.79 with the exporter/importer...And try to export it with this version/addon (see below). i think you have import this model, right? Or have you animate and create it by yourself? When you import a extern model, i cant help you. You can try to create a cube, animate it and export it to ensure that your model isnt/is broken or you export the model on the wrong way(I am not using blender 4.0 and i dont useing mdl editor etc...).
It seems to me that your model is broken.
(I am using Blender 2.79 for my models and my animations, because this version works for my mdl exporter. I only know the abolsutley basics. For my Animations and export:
(1. Create a Model
2. Create a single Bone
3. Selekt the Model and the Bone
4. Go Objekt -> Parent -> with emty groups -> with empty group
5. go edit mode -> objekt data (near Materials)
6. Select faces and -> Assign (for attach vertex/faces to the bone)
7. go pose mode and animate your model (move the bones). Set Key with hotkey I: lokation, rotation, scaling for your movement.
8. for export the model WITH animation you must set marker (maybe the problem here?) press m in timeline to set a marker rename it with strg+m to your animation (stand) or (attack)
->Example: stand animation from 0 to 1000, set marker at 0 and name it stand and set a marker at 1000 and name it stand
9. Go objekt mode and select your model. than export it with mdl-exporter-2.79.)
Maybe it can help...indirectly