Every time I open the saved file, some of the fonts change to the default font, and I have to manually adjust them to the fonts that were previously set. It feels really inconvenient.
What file type are you using? .odp? .ppt? .pptx?
I always use .pptx. So that I can share file with Microsoft Office users.
There is not (never was and never will be) 100% compatibility between the different filetypes. You always will lose some formating properties or even some content when you cunvert the documents into a foreign file format. Save your documents into the native, international standard ODF file formats.
MS Users can open the ODF files with the MS Office, or even they can install the free LibreOffice.