Why do my Gnocchi get sticky?
I made gnocchi for 2 years at restaurant... in those two years i observed to following things about making gnocchi.


the type of potato Changed the ratio of flour, and egg if using egg.
 As i am living in the Southern Arizona. I settled on using the Classic 1 lbs Russet Potato. 
the size of the potato and how long and at what temperature you bake it... I have tried everything from purple fingerling potatoes to Sweet potato. they key i found was to try and cook them in a way that they released as much moisture as possible... I settled on baking my potato whole at 425 degrees F, lightly oiled, for 45 minutes in a convection oven on High Fan. when they were done, i would cut them in half for ricing and let them cool for 10-15 minutes, this would allow for the potatoes to release a lot of steam/moisture.
Getting my ratios right...I tried everything under the sun....i settled on a 1:1:1 ratio i found in an old Italian cook book... that would be 1 lbs riced potato, 1 egg yolk, and 1 cup flour....I did use rice flour on occasion if there was a gluten free customer...they were a little weird but not to bad. The key was not to mix more than you had to.
cooking/storage... as i was producing 50 portions 1 per week. I would toss the portions lightly in flour then freeze in deli containers, then boil off and toss in a pan sage butter similar to what you do. I seamed to work... as we had 8 different line cooks who mad this meal sometime there would be circumstances like your where they would stick together into a Gnoccho...Large Lump... i found this was mainly because they did not change out the water they were being cooked in... or the water was too salty, boiling temp lowers when salt is added.
any way... hope this helped....