space changing between paragraphs without command problem

Hello. I have LO 5 and Ubuntu 16.04. Unfortunately there is an issue regarding the space between paragraphs, namely when I create paragraphs without giving tab on the first line, (all lines full), after closing the document and reopen it, there is a huge space between two paragraphs without being set by me. On the contrary, when I use tab on the first line of each paragraph there is no such a huge space, when the doc is reopened. Could be someone so kind to solve this issue, because I do not use tabs! Thank you in advance!

Which version of LO5? Which paragraph style do you use for the paragraph? Do you use an own document template? Help would be easier, if you provide such document for download. Besides, there is never a reason to use a tab at the beginning of a paragraph.