I’m having issues with getting the model CFrame of a sword welded to my character. It does not stay up to date and will freeze in one spot.
However, if I make my camera collide with my character, the cframe updates.
Deselecting and reselecting the sword in studio does not update the wireframe. Even using :GetModelCFrame() will give an out-of-date location (as you can see i tried with the two 1x1x1 cubes in picture 3)
Maybe it’s all the welds?? But the sword visually looks fine. 
Well it is depreciated
What I would do is make another part at the center of the model and weld it in and set it as the primary part then just use GetPrimaryPartCFrame ( )
Had this issue so I just stopped using welds. I’m almost certain this isn’t on your side
Were you using GetModelCFrame as well, or is the regular CFrame of the parts not even updating?
Both. I’ve had this issue for over 4 months I believe and was the primary reason for me switching from welds to CFrame for animating.
oops. I’ve been absent for a year I didn’t know it was deprecated 
There seems to be a bug with bounding boxes and physically simulated objects. I’ll put a ticket in for this.
Please don’t use deprecated things. Thanks <3. (GetModelCFrame)
There’s not an alternative to finding the center of a model. PrimaryParts are not alternatives because they still have to be manually placed – how can they be placed at the center of an off-grid model if we don’t know the center?
You could do your own bounding check by looping through all the parts in a model and checking the furthest extents although that might make you want to take a shower afterwards. GetModelCFrame still has its use just don’t rely on it because it is deprecated.