With over a decade old experience being a seller (wordpress/programming) at Fiverr with a fair share of orders as well I always appreciate the change for the good but unfortunately, there is nothing good about this biased change letting user review after the cancellation as if cancellations are the sole responsibility of the seller.
So far cancellations are always considered as the seller's fault and each cancellation affects their Order completion rate which again affects the quality of the gig traffic they will get and they are forced to keep up.
My concern is why the Buyer gets to review after the cancellation and why not the seller as well. Who will decide if cancellations are the sole responsibility of the seller and not of the ignorant buyers who place the order and then clarify the requirements (this happens a lot in programming gigs where the gig is a service and not a product) because they couldn't spare a min or two to read the gig description or are sometimes clever enough to ignore it intentionally to get more out of the order because they know once the order is placed seller will be compelled to deliver and after this change, they get a free blackmail review if the seller doesn't comply to their unreasonable demands or extra work.
My suggestion is Fiverr shouldn't harass sellers with cancellations or feedback on every cancellation and give them a few cancellations per month (even fair if based on the order completion rate of last month) without a consequence whereas more than a few should be fair to affect the reputation or invite feedback from buyers or be taken under review by Fiverr.
I am a victim of this blackmail for over a decade and Fiverr's policymakers have to think out of the box that not all gigs are under the same category, and not all of them are sold as a product a lot of them are services as well and they should be treated as one.
So, a thumb rule cannot fit for all.