Thanks for the post!
I'd be interested in seeing the SIDB Engine logs before and after, even a few weeks before to see if there is gegredation over time, or if it's only right after the update.
No doubt a new store will be fast, though you've mentioned this is recurring for you.
How long in between updates are you going? Was there an upgrade from 14 to 17 directly, or were there updates in between? If so, was there slowness there as well?
Some contextual questions, if you can:
What is the speed/throughput before and after?
Can you run some Job Summary Reports for the Aux Copy jobs leading up to the seal/update so we can chart it out, and check the actual update date?
Are there multiple Storage Policies with Dedupe? If so, is it consistent across?
Don't want to jump to assumptions without seeing the evidence first.