It's most likely to be frilling of the edges of the emulsion. Tiny particles of emulsion coming off the edges of the film, any undue temperature variations between Dev, Stop, fix, wash etc will exacerbate this. EFKE films aren't particularly well hardened so a re prone to theses problems. You can use a pre-hardening bath before developing, some are listed in the Darkroom Cookbook, (the 3rd Edition is out very soon).
Using a tanning developer like Pyrocat, or PMK will help too as the Pyrocatechin or Pyrogallol tans & hardens the emulsion. If you've processed EFKE films its worth filtering and solutions you're going to re-use.
With good tight processing controls particularly with solution & washing temperature you shouldn't get a problem.