I agree that that is a likely source of the cloudiness, but I don't think incomplete fixing is likely to cause the emulsion to rub right off a modern film, unless the films were actually put away wet. The OP says that they develop carefully at 68 degrees; I may be splitting hairs here, but that doesn't tell me about the temperature of the wash water. If you wash in running tap water, it is sometimes easy to lose control of the temperature. Hot water could physically damage the emulsion.
Hi, thanks for your thoughts. Final wash was at tap temperature- its possible that the temperature exceeded 76 degrees, Another fact is that the tap water is hard in this part of the world- though I don't suspect this to be a source of the issue.
Finally, if heat damaged the emulsion during development, then the emulsion should have been soft after development when I ran my fingers down the length of the reel to get excess water off. Since there is no obvious physical damage to the dried negatives, its hard to imagine heat during original development being the issue.
Finally-and probably most importantly- what can I do, if anything?
Would a hardening fixer help in this case? I found a few hardening options on BH- I could give it a try.