Don't know if this is still issue or not but here are some comments:
I have not tested any of the topologies you mention:
4x2x1
7x2x1
36x3x1
The largest torus I've verified is 10x10x10.
These are all 2D rather than 3D tori. Note that a 2D torus must be configured with either the x or y radix
as 1 (i.e. configured as either a 1 x m x n or a m x 1 x n torus).
Also, the ones which are 2x1 are limited in fault (link or switch failure) in dimension with 2 switches but this has nothing to do with credit loops in non faulted case.
Looks like you are used MLNX OFED OpenSM. There have been a number of fixes/improvements to torus since the one you are using. If this is still of interest and still a problem, I would recommend updating to the most recent version (either MLNX OFED or upstream (latest 3.3.18 release) and retrying this. If it's still a problem, would you post your ibnetdiscover output and the OpenSM configuration ?