I have recently migrated to LibreOffice (LO) 6.0.7 from LO 5.4.7. I edited an ODT file of around 4MB, containing around 100 pages, and saved it. To my surprise, the size of the file went up to around 15MB. On top of that, it takes now much longer time to close or open it (more than one hour). The size increased even after deleting some texts. I also tried this with LO 6.1.3, but the result was the same. With LO 5.4.7, the file can be saved or opened less than one minute.
I cannot attach this file for the reason of copyright, but it is a booklet with some photos. A table of content is being automatically created and some words are indexed.
I would be very grateful if you could advise me in this matter so that I might duly open and save this file with LO 6.0 or later.
[Enviroment]
AMD A10-7860 3.60GHz, 8GB, Windows 10 Home 64bit, Java 1.8.0_131