Hey guys, sorry to (sort of) necrobump this, but improving on this previous answer:
For some reason, this flickering happens after the ribbon lifetime as the lead particle (or system?) dies out, and by allowing the system to Complete we’ll probably see this bug.
What did work (as in workaround, not fix) consistently for me was also setting the inactive state to Kill:
https://forums.unrealengine.com/core/image/gif;base64
These trails were flickering like crazy before the fix: