Wait a few minutes for the device to come back to normal temperatures.Make sure to sign in using the same Apple ID on every device. I think I've observed slowness more frequently when running the app from Xcode, but I'm not positive that could be a factor. In the Messages app on your Mac, enter your Apple ID and password, then click Sign In. If thats the case, then select select your phone number. It could be because of additional system load, memory pressure or other reasons. Open Settings > Messages > Send & Receive and check to make sure the same Apple ID you used on your iPhone is being used on your iPad. I believe in those cases the ANE is not engaged and all the work is done on CPU. When generation is slow, the phone heats up a lot. Are those results consistent across runs? I've seen some erratic behaviour on iPhone myself – sometimes it's very fast and sometimes it's slow, with no changes in model or configuration whatsoever. Open messages on your Mac computer by clicking on the green message icon in the menu bar.

Go into the Settings app on your iPhone, then scroll down until you find Messages. Ensure that your iMessages appear on both your Mac and your iPhone. Hi sorry for the delay in getting back to you. AppleInsider shows you how to set up the feature and get messaging on your iPad, Mac and more.

How to link macbook and iphone messages