Many times when a system is repaired the owner doesn’t want to spend much money. Often time the repair system is smaller than the initial system. Also your tank is under sized. Does it have a baffle and an outlet filter? A larger tank with a baffle helps to separate the solids and liquids better. The larger tank also gives grease time to separate from the water so it will rise to the top. The baffle and outlet tee or outlet filter prevent the grease from going into the drain-field. If you have a garbage grinder the tank will fill up quicker and clog the drain-field sooner too. Sometimes roots can grow into the drain-lines and clog them up. Plants like wisteria can clog them up fast. There are many things that can cause a failure such as being undersized, located in a bad area, put in too deep or a bad installation etc. Sometimes the cable company will damage the lines etc.