I have a known bug (outlined here, here, here, here, and here) where burst photos won't delete.
I suspect instructions here would help, except my problem is more complicated since the bursts are not in Photos, but in 'Recently Deleted'.
Also, I have Emptied 'Recently Deleted' many times, so the files are still there, but they appear blank, so I cannot tell which of the 25000 files are bursts (there are 17 sets of bursts among the 25000 files).
Attempts to 'Delete' the files from 'Recently Deleted' results in them simply reappearing after exiting and reentering 'Recently Deleted'. Attempts to restore them results in blank files going back into Photos, with no way of distinguishing the bursts from the regular photos.
Best Answer
How to solve:
The steps to delete an individual burst from Photos are
Repeat the above steps once for every burst you want to delete.