I have this same exact problem and could not find a resolution to it. My only conclusion that it's obviously a bug with newer builds of 2017 and maybe hardware. I've tried different video both 4k and 1080p, shot with different cameras in the past that I've used in Premiere without a hitch. I've encoded it in different codecs which ended up being a waste of time anyways as it still yielded the same results. I primarily use SSDs for storage of my source footage but I also have a fancy newer M.2 SSD. Doesn't matter what drive it's on it'll still freezes in the timeline when I hit play. Then at some point the application becomes mostly unresponsive, I can kinda scrub through the timeline but its clunky and frustrating. One interesting thing I did discover is if I roll back to a previous build of Premiere 2017 (11.0.0) or any of the builds in-between the current one the timeline is actually more responsive and I can somewhat edit the timeline but still when I hit play it freezes (staying on the current frame but acting like its still playing). My only solution to fix this so you can keep working is to go back to Premiere Pro 2015.3 (10.3.0) you can do this in the Creative Cloud app under Find Additional Apps under the Apps tab and click on View Previous Versions to the left. You should be able to find all the previous builds of Premiere Pro all the way back to CS6. In 2015.3 I have no problems what so ever like I used to and all my footage plays just fine. Even the 4k footage is handled just fine. I can get back to work. The only downside is if you have previous project saves in the later builds you will have to start new and re-edit it as it won't support newer files of course. Try going back to 2015.3 and let us know if you still have the problem. My Hardware: Intel Core i7-7700K CPU @ 4.2GHz Oc'd to 4.7GHz 64 GB DDR4 3400mhz 2x Nvidia 1080 GTX Sata SSD storage and m.2 SSDs Windows 10 latest build
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