Russian is hard, remember that! You have done a ton of progress. I know how that feels and you should know its completely normal.

I don't know specifically about russian, but I recently went "back" and just bought a book from a lower level and did the exercises everyday after work. I feel more confident and learned some words that I had somehow ignored or missed.

Might not be feasible for you, but my advice is just exercising, looking up words you don't know, write a short sentence with a new word (on paper, with a pen) and if you are missing some grammar rules you know of, look that up too.

Language learning as an adult is tough, but with discipline you'll get through.