“Read More” not showing up on category main page

I have tried a number of new themes and I notice a disturbing trend. If I create a long post, and the click on the category that that post is listed in, SOME of the themes will automatically truncate the post (whether or NOT I’ve used the “spli post” option) and just put […]. The only way to read the entire article, is to click on the post name. however, if I go to the Default Theme, or the classic theme, then entire article is displayed under the category. If I use a “split post” the Classic and Default themes display this correctly, but the Bluezine and Handy MAn themes have a problem with this? IS there a way to fix this? I have tried other themes, some display the whole post, some truncate them and leave just […] and the three dots are NOT a link. Any ideas?