I made a simple 6-faced poly strip and polygrouped the top and bottom to make a simple TRI IMM strip.
The problem is auto-groups turns that into a checkered polygroup mess. It essentially polygroups the repeated parts.
Weld points is checked. The strip itself has no disconnected verts. The tri button is on, along with all the other typical IMM options. Nothing works. I even tried disabling the TRI option and just made a simple strip polygrouped together and it still does not work.
What Ive noticed is a flat EXTRACTED plane autogroups correctly. An IMM flat plane does not.
However if I take that very same plane and extrude it into a thick poly strip, autogroups works fine.
So why doesnt autogroups work with flat poly strips? I never read anything that says it needs to be a little thick for autogroups to work correctly. Ive tried the zmodeler polygroup-island option and I get the SAME results. Its as if for whatever reason my IMM is constantly split in tris, regardless of what options are set.