The best work around for this is actually to:
Select one product.
Choose "Select All"
Deselect a single product.
Delete 49 products at a time.
NOTE TO SQUARESPACE:
Learn to use arrays properly! This bug will be down to the misallocation of indexes in arrays.
Also, 50 at a time when the platform can handle 10,000 products?! Fix this. Now. Please 🙂
Also. Allow for bulk image updates in import/bulk edits. That is all.
cya