It is crucial on Hive to source your materials that you did not write. If you start doing that it's not considered plagiarism. Even pulling small sections from your papers you got to cite them. I'd suggest you put links on the bottom even if its your own writing if you were using other sources to start from. Probably a good idea to cite them.
It's unfortunate you had to learn the hard way. Usually it's been the job for your mentor here (person that introduced you to Hive) to point out these things so you do not get hammered by HW.