4th gen recording on HDD problems

I tried to search to see if this problem has been brought up but not the most robust search engine so apologies if it has.

4th gen that works perfectly off the internal storage for both viewing and recording but wanted to expand storage. Added a 2TB Seagate external drive, formatted it and scheduled some shows to record. They recorded but if there is any kind of fast action scene, it starts to slightly stutter. Now I’ve plugged in a Nvme SSD drive with USB adapter and it plays perfectly. Does the HDD not have enough bandwith/speed to work or have I not set up something I should have? Will use the Nvme but it’s only 500gb and I know they aren’t recommended for longevity.

Thanks for any guidance or help.

What model Seagate drive is it?