The good news is that the sunk cost for learning a language isn’t completely “sunk”. You will have some retention no matter what, so resetting isn’t always a bad thing.
Set a day, stop doing lessons, and then just knock out as many as you can per day. I crawled back from a backlog of 1400+ items so it’s doable, just painful. 
That whole experience is what made me settle on the limit of 100 Apprentice and 500-600 Guru. With these numbers my daily load is kept manageable but I’ll also delay starting levels if I need to lower those numbers.