We have heard very few such incidents the past few months versus it was very common last year the first few months after merger.
More often than not, the incidents were false alarms due to the Marriott site is not intuitive and customers are confused / not knowing how the system works (not in a good user friendly way that is for sure.)
You need to keep track of the TOTAL BALANCE to actually know whether the points are refunded or not.
Personally I take snap shot of my account activity every now and then, esp if I have a lot of redemption / cancellation in preparation of a trip. I dont keep a spread sheet which is reserved for HH due to their confusing double entries at booking and at staying, makes it look like they deducted the points twice but in reality, the deduction is only performed at booking, not at staying despite the account activity shows otherwise.
Marriott does not have this issue but the refund entry format is much less than desired.
Marriott site does NOT do in and out entries on canceled award stay. It would just make the initial booking cost becomes ZERO versus the deduction. You do NOT see a "put back" entry of your points, but essentially it is "put back" because the original deduction is ERASED.
This is how it looks like in my account on a 5th night free of 70K pts award stay -
06/06/2019 Rewards Standard Redemption Rate
06/06/2019, Cancelled 0 Rewards +0 Points
The 70K deduction was erased and 0 Points shown.
My total balance went up by 70K when I looked at the side bar, before I logged out of my account, before the cancellation email hit my inbox.
An earlier example that involved 140K pts, same thing.
03/28/2019 Rewards Standard Redemption Rate
03/28/2019, Cancelled 0 Rewards +0 Points
Your total balance should have gone UP to incl the refund of the points. But if you keep looking the account activity without thinking about your account total balance, you would have thought that your pts were not refunded.
Go back to find the original redemption entry and see how it displays the points - should be a 0.
High probability your points have already been refunded. Check the original deduction line, and see what is the number shown next to that line entry - is it now Zero, or still show a -17,500? If it is Zero, your points have been put back to your account.
FWIW, Chase Ultimate Reward Point Bookings employ the SAME mechanism of Marriott site - you do not see a "put back" entry, but rather the original deduction is erased. The point balance goes up within the same session but you may need to move around the site a bit in order for the screen to update.
I have found Marriott site behaves very similarily.