Keep a list of small features/tweaks to the side and use them as jumping off points. Takes a little bit of forethought, but I keep a txt file in the repo with a list of things like class implementation tweaks or ui changes that I know are 15-30 minute tasks. I reserve these for when I'm having trouble ramping up.
Or failing that, 15 minutes of cranking out garbage code that I know I'll revert helps get back into flow state too, but it's demoralizing deleting work.
It might feel demoralizing but writing and testing out throwaway code is part of figuring things out. Writing that code helped you get to a point where you have better insight.
Or failing that, 15 minutes of cranking out garbage code that I know I'll revert helps get back into flow state too, but it's demoralizing deleting work.