Since it appears that you have a mixed mode mesh between beams and at least one shell (or solid) for the top plate this bug/issue likely applies:
SPR 932412: 'Find underconstrained bodies' tool shows wrongly constrained beams as underconstrained when used in a not a pure beams model including other kind of bodies (e.g. solids or shells)
So, it would appear that you should ignore this body and try running your analysis to confirm whether you have an instability or not.
okay, so if I do run a study that fails and the unconstrained bodies check shows results that appear to be illogical then most likely my problem lies somewhere else in the model? That could help me at least find the faulty body. Ill try it out on Monday, thank you!
Yeah, the issue likely lies somewhere else. There is a pretty easy way to find it though; it is the old way people used before this constraint check was put into the software which is this:
1. Go into the study 'Properties'
Enable 'Use soft springs to stabilize model'
Disable 'Compute free body forces'
Disable '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 calculated so far.
5. Inspect the displacement plot in the results to find the unrestrained body (you may need to disable the deformed shape of the plot as some bodies my be visually very far from the rest)
Other older options are also detailed here (GoEngineer - Simulation: Tests for Unstable Studies).