I was having a lot of trouble with motion on my 65" set, with what looks like judder and frame drops to my (admittedly untrained) eye, from external HDMI sources – specifically a PS4 Pro and a Roku Ultra (used for testing). I got in touch with TCL's support regarding this, as well as lip sync issues over ARC to my Yamaha YAS 108 soundbar (I tried switching the output to PCM STEREO, didn't work), and they asked me to send them a couple of videos of the problem. I made them the following two using the PS4, although the same issues arose on the Roku:
Into the Spiderverse on the Netflix app: https://imgur.com/IfiwiIB
Undone on Amazon Prime: https://imgur.com/KEReEF5
They were very friendly and responsive and told me that they escalated the issue to their engineers, and yesterday I got another email from them, telling me that Roku should be releasing an update sometime next week to address both issues. I also experienced a similar situation as someone else posted on here, where Game Mode for some reason helped with the motion issues, even on the external Roku Ultra, and notified TCL of it, although I didn't get much response on that.
Anyway, don't know if this is helpful info for anyone out there. I personally hope that it gets resolved because I'd hate to return the set. Love the colors and haven't been totally sold on the H9F for that same reason, although that's obviously a just a personal preference.