Often controllers file 'overload' reports, only for the investigation to conclude that an overload didn't exist purely because the sector flow rate was not exceeded.
Wrong, if a controller files an overload report then they are without question overloaded even if the sector flow rate wasn't exceeded. If it was a case of the sector flow rates determining overloads then when we try out a new higher flow rate and an overload occurs, you'll be told it was within rate and the rate not adjusted back down. Don't forget that controllers are all just human and that on different days we can handle different levels of traffic just due to how we are on that day, and another controller could handle more or less during the same session due to personal competence, so if anyone feels overloaded its not a personal 'failure', just maximum level reached. Overloads do often occur due to bunching as mentioned above, but also due to presentation from other sectors, late offers of traffic, and even bad RTF management on both ATC and Pilot sides. One of the ones I had delivered under sector capacity over the hour period, unfortunately 50% of that sector flow rate came together on the same route 10nm wide within a 20 minute period, at one stage all a/c were within 25nm of each other, and all needing level changes.
With regard to sectors being bandboxed or split at certain times of the day, you'd be suprised at the times sectors get busy ie S15/16/17 (DVR in old language) at 10:30 in the evening, and Clacton at the same time with all the Ryanairs and Easyjets returning to base mixed with the last European and all Middle and Far East flights departing. If the sector looks like it should split then normally it will. However sometimes there is little warning and we can see its a short burst so by the time the split happens all the traffic has passed.
If you as Pilots feel that the frequency is far too congested then I would say you should file an MOR. If only one or two are filed then nothing will ever change, but from reading others threads too, its becoming far more common that the RTF is getting saturated. What happens if you have a Mayday? Yes by selecting 7700 we'll see you have a problem, but then what about all the other tracks as you are dealt with? If you file an MOR and the controller has missed a readback or two, then its not nice knowing that they will be investigated, however they may not realise they had done and by finding this out they will only learn how to be a better controller, as incidents improve our experience and make us better next time. The only thing I do ask is that you do not tell the Controller over the frequency you are filing (had this twice now) as it congests the frequency, can stun/anger the controller, and is much better to give the centre a call upon landing for a quick word with the Watch Manager/Supervisor. Even though the RTF may go quiet after a busy spell it doesn't mean the situation is over, we could be on the telephone or giving a handover to a fresh controller and unneccessary interuptions only hamper the smooth flow.