I checked it myself using a database for learning English . As a result, the amount of outstanding repetitions grows quite quickly, and sessions get longer and longer. Tiredness and lack of time come into play, and we begin to skip some sessions. The outstanding repetitions will double if you skip two sessions. Naturally, this is not an accusation of the method or the program.
Regular repetitions are necessary for success.
In the same way like turning on the gas is necessary to boil water to prepare a cup of tea. I think it should be possible to automate such situations. The program should be enhanced by an option that would help reduce the amount of repetitions by removing or postponing best-remembered items.