The main problem with emergency egress handles (and manual cab egress handles) is the wear and tear on the cable mechanism. If that breaks, or the cable is stretched by overuse and does not happen to get seen to by a depot in sufficient time, then the door can potentially become unusable and may get stuck in a given position. This causes a number of delays each year to most operators of modern stock. (It's also why I dislike the Turbostars which don't have air-assisted cab doors, because if they are on busier routes and have to be worked from the rear or middle cabs by guards, the wear and tear on the cab door handles at each stop could be quite intense. This also applies to all the older Electrostars, to a degree.)
I would hazard a guess that the 700s count the number of times that the manual egress system is used, and they throw wobblies if the system is used too much. If these errors are related to the difficulties I've described above, this is for a very good reason.
I did read the original operating instructions to platform staff, though I don't have my own copy to hand, and I'm sure the details were that the train doors should be locked out of use but with one panel active (the GOP, or guard's operating panel, which on 700 stock is able to control its own local door, all other doors and indeed the PA system). Passengers remaining on the train were then to be detrained by walking them down to the local door by the GOP. At the end of the process, this would be the final door to be locked out, and then the train could proceed empty to depot.
Unfortunately, there are some locations where the station staff who lock out trains are not safety-critical, which does seem to apply mainly to the Southeastern network. Where this is the case, I can't imagine they'd be given access to the GOP train door controls. On the other hand, emergency egresses are designed for anyone to use in emergency, so they could have come to the conclusion that those are to be used instead. This bit is just speculation, but it may be what's happened.
I can't comment about "software" based emergency egresses, where the doors can't be automatically released and a different method is needed for the driver to manually select the way the doors are to open. There is certainly a function to do this on the likes of the 377s, and from experience this operation can be carried out from the Mitrac computer many times without the system locking up, although there are nuances to the system which take some getting used to.