It does seem that transferring points is qualifying activity. I sent an email to Hyatt and got the following response:Dear Mr. Osaka,
I would like to inform you that Combining or transferring points to another members counts towards an activity.
Should you need further assistance, please let us know.
Thank you for your loyalty!
Best regards,
Eunice xxx
Hyatt Care Team | Global Contact Centre

I just transferred points to MrsCP and AwardWallet says both have 2 years to expiration, probably based on most recent Activity date (as Hyatt has no available "points expiration date" field, apparently).

Interestingly, instead of removing ~10K from mine and adding them to hers, they added 10K to both accounts. My expiration date was tomorrow, so I guess I'll see soon if those points disappear in a day due to expiration. Unless they realize the error and zero it out - but based on the transfer competency, I doubt it.

Fwiw - I had read "3-4 days to transfer" in posts here, so I completed the form on the 11th. With a 6 day response time, and multiple un-documented requirements requiring an update, the points transferred today, a day before the expiration.

Now 3 days past the 2-year mark since my last stay/activity, and I still have the points.

So the transfer Activity seems to have qualified to reset the clock.