New October 2015 iMac El Capitan 10.11.3

After streaming Netflix on mini port HDMI connector to thunderbolt the cursor freezes. This is the second iMac in 6 months that had the same problem. The other iMac which we returned was a June 2013 model...
el Capitan 10.11.1.Are iMacs not compatible with Netflix?

Welcome to the forum. What does this mean?

on mini port HDMI connector to thunderbolt

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What display device? I'm confused. I've watched Netflix on iMacs for years without any problems, but I've always used the iMac itself to watch.

In your return post please add what iMac you have so we can get a focused solution for you.

I have an iMac released in Oct. 2015. I purchased it on Feb.11 2016. It already had El Capitan 10.11.3 loaded on it.I stream Netflix from the new iMac to a Toshiba wall screen tv.
I also have a 2008 Macbook Pro that I have used for streaming Netflix. I have had no problems with the cursor on the laptop.When I set the new iMac up, I did migrate my backup information from my Time Capsule.

Did you add any software to the iMac? Antivirus/helper/cleaner/booster utilities? You don't need them, and some of them are problem children. Also, what mouse/trackpad? There are a lot of places where the mouse can go awry.

Yes, I did download adware because of popups.

Which adware blocker did you download? Try disabling it for Netflix and see if that resolves the issue.