This is a common question that comes up a lot on this forum. The model is definitely unstable but tracking down how it is unstable is the real problem. I went through a quick stability diagnosis in a duplicate of your study like this:
1. Go into the study 'Properties'
Turn on 'Use soft springs to stabilize model'
Turn off 'Compute free body forces'
Turn off 'Large displacement mode'
2. Suppress all loads and apply only 'Gravity'
3. Mesh/Run the study
4. When the solver stops (if it stops) due to large displacements and prompts to put the study into 'Large Displacement mode' declined this offer. The solver will dump what results it has so far
5. Inspect the displacement plot in the results to find the unrestrained body
The results showed several bodies were not attached to the main structure:
You may want to create specific bonded contact sets attaching these pieces to the main structure.