There's no doubt of the existance of micro/surface reticulation, it's why Ctein wet mounts his negatives against glass for printing and why high end scans are wet mounted as well, something that was first done in the 1920's to reduce the grain in enlargements from 35mm film. It's not "Grain clumping" in the film though it's the effect of irregularities on the surface of the filmcausing increased ggraininess in prints and particularly scans where it shows up more.
Gerald Koch is right that true reticulation is almost impossible to induce with most modern films and newer hardening techniques have made micro/surface reticulation a thing of the past with many films. Neopan 400 and the older Tmax 400 can suffer this surface effect which became a problen with the advent of the firts digital minilabs prints made with the films of the time were grainier than optical prints. Kodak improved many of their films and the new datasheets & press releases state the films have been improved for scanning.
However there are other exceptions and films from some smaller manufaturers like Foma and particularly EFKE have less hardening. EFKE films will reticulate and even slide off the base.
Rodinal in particular can increase the likelyhood of micro/surface reticulation because of the free hydroxide it contains, most cases with Neopna 400 that people have reorted have been with Rodinal.
It's not the film/developer combination itself that's the cause it's poor temperature control throughout the entire process cycle.