I had a Hoover which would do the same, seems before we had bought the fridge freezer it had been damaged, a new outer shell fitted, but the insulation had also been damaged, there result was over time ice would build up in the cracks, and allow heat to get in, and this resulted in ice building up in parts where it would not normally build up, which would stall the fan, which in turn would report and error, we would empty the unit, and call in the contract repair man, who would change some part, and say it's OK now.
This went on for years, the fridge freezer was likely 10 years old, when we did not have time to empty the unit, the repair man looked at the build up of ice, and said insulation failed, I will write a report and you will get paid out, which is what happened, we then moved the old unit into the garage, where it was used to brew my beer, and likely would have continued to do that for another 10 years, but on moving house we got rid of it.
We were lucky we had taken out a maintenance contract, I have an energy monitor that I move around now freezer to freezer, it was on my chest freezer, now on upright freezer.
bottom left you can see the near straight line for chest freezer, and the sine wave where the auto defrost cuts in with the upright model. Top right you can see how the unit is switching on/off, so average around 35 watts, so that means around an annual use of 306 kWh, the advert says a new one should be around 250 kWh/annum, this is the hottest time of year, and always seems to show using more than it says it should, so seems at 8 year old not doing bad, the energy monitor does seem about the best way to judge how well it is doing.