Description:
I had to save my spreadsheet in xlsx format to enable upload to a site. When it is saved in this format a blank area appears in the first approximately 51 rows (sometimes up to 59 rows) obscuring any text I may have in these rows. As a work around I had to 'Insert rows above' in order to shift my text down and see it. If i attempt to delete this blank area I find that there are multiple of these blank areas stacked on top of each other, sometimes i may have to delete over 20 of these to get a 'clean' spreadsheet again. Unfortunately they re-appear should i close and re-open the .xlsx spreadsheet at a later stage. I am currently using Libra Office 6.3.2.2 and i had this same problem with previous versions of Libra Office. I do not have this problem in .xls format, nor in MS Office.

Steps to Reproduce:
1.Open my .xls file
2.File > Save as... 
3.Go to Drop down window below right 
4.Select 'Excel 2007-365(.xlsx)
5.Save

Actual Results:
In most of the spreadsheets of my file I had the blank area appear in the first 51 - 59 rows, obscuring my text. 

Expected Results:
I expect to see no blank area to appear, rather i expect the spreadsheet to appear exactly how it did in .xls format. That is all my text showing clearly with no 'blank area/s' (or text box/s) obscuring my text.


Reproducible: Always


User Profile Reset: Yes


OpenGL enabled: Yes

Additional Info:
The forums are not much help, a moderator even closed the topic for no good reason, e.g. https://ask.libreoffice.org/en/question/9458/blank-box-areas-appear-when-trying-to-print/
I can provide you a copy of my file so that you can see what the problem looks like. 
My problem is not related to Userprofile: I always had this problem across a number of PC's
My problem is not affected by OpenGL, here is my details if you require:
OpenGL vendor string: nouveau
OpenGL renderer string: NVA8
OpenGL core profile version string: 3.3 (Core Profile) Mesa 19.2.1
OpenGL core profile shading language version string: 3.30
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile
OpenGL core profile extensions:
OpenGL version string: 3.3 (Compatibility Profile) Mesa 19.2.1
OpenGL shading language version string: 3.30
OpenGL context flags: (none)
OpenGL profile mask: compatibility profile
OpenGL extensions:
OpenGL ES profile version string: OpenGL ES 3.0 Mesa 19.2.1
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.00
OpenGL ES profile extensions:

Help - About LibreOffice:
Version: 6.3.2.2
Build ID: 1:6.3.2-0ubuntu2
CPU threads: 2; OS: Linux 5.3; UI render: default; VCL: gtk3; 
Locale: en-ZA (en_ZA.UTF-8); UI-Language: en-US
Calc: threaded