I've tried it with stock internet explorer as well as many other browsers on different computers.
It seems to be a browser-independent phenomenon.

Shop through chase activity is definitely missing on my page.
It seems like a glitch that is rare but not specific to me.

The page that should show shop through chase activity is:
https://ultimaterewardspoints.chase....wards-activity

For those of you with working Chase accounts, it should show the activity toward the bottom of the screen after you scroll down to the end of the "Most recent activity."

But on mine, it is gone.