In spurts
Definition 1 of 1
Pro Tip 1/3Irregular Patterns
Understanding 'in spurts' means recognizing the action doesn't happen in a regular pattern or at predictable intervals. 
My sister's interest in painting comes in spurts; some weeks she paints daily, and then not at all.
Pro Tip 2/3Sudden Activity
'In spurts' conveys a sudden increase in activity after a period of stillness or slower pace. 
The old car started in spurts, sputtering to life after being unused for a while.
Pro Tip 3/3Common Misuse
Don't confuse 'in spurts' with consistent, ongoing progress; it implies intermittent bursts of action or growth. 
Her blog gained popularity in spurts, with periods of rapid follower increase followed by quiet.