I had a fridge/freezer on maintenance contract, it iced up within the year, and first time before I realised what was happening it stopped the fan running in freezer with the ice, we had people out to it around 5 times in it's 15 year life, each one would fit some thing and we were glad we had the maintenance contract, but would always de-frost first as normally that would fix the problem, until the last time when rather busy and did not defrost, the maintenance guy opened door looked at it and condemned it as uneconomical to repair.
It seems the insulation had been damaged, likely from new, and ice builds up inside the insulation, and ice conducts heat better than air, so it was running inefficiently due to ice build up, the guy had seen it many times before and knew straight away what the problem was, so best option is to monitor power used.
Most fridges and freezers have an annual power usage, so if it says 365 kWh then one should expect it to use 1 kWh per day, at 1.2 kWh no real worries, but by time it hits 1.5 kWh then clearly some thing wrong.
I did the test on all my units, and mothers freezer had a 65 watt motor, and in 10 hours used 650 watt/hours, it turned out thermostat faulty, was cooling to -24°C not -18°C which explained why the ready meals had cool centres when cooked.
Fridge normally 4°C and freezer -18°C so should never get ice in fridge, some thing clearly wrong, could be simply set too low, but you need to test.