I thought all the LaBella flats were hex core before these new strings came out
I tried round core DR flats that had rough looking windings and saw others with similar issues. The TIs also have the layer of silk thrown in between there. I don't think the new low tension La Bellas have that.
I doubt LaBella uses a silk layer, but that has nothing to do with the bond between the core and windings. That's done by tiny crimps. I've used LaBella DTB flats on one bass for years, never a problem with separation, roughness or any other issue. LaBella does recommend against using DTB flats strung through-body because there are several flat windings and a sharp bend can cause them to break.
About 10 years ago I called LaBella with a specific question and wound up having a nice conversation with Bob Archigian, their longtime national sales manager. Among other things he told me that the DTB flats and rounds were round core and that the Hard Rockin' Steel rounds were hex core. No big deal to me either way.