hi, im writing some formulas on libreoffice, and it`s look good:
but when i export it to pdf, its looks like this:
i have open symbol font installed on my pc…
please help, thank you 
I have the same problem in Lubuntu 18.04. In my case, the reason is “Right-to-Left text direction”. I tested it in one document with both right-to-left and left-to-right directions. As you see, only right-to-left ones are not printed properly.
It is worth mentioning that I only used the following formula:
E=mc^2
i have same problem in ubuntu 19.04