Since updating my libreoffice to version 5 (and Windows to 10), text portions in sanskrit fonts are not showing properly, all characters are replaced by squares. The text portions in regular latin letter fonts are showing fine as before. Yes, the fonts are installed correctly, they appear in the list of fonts and the same font looks fine in WordPad. The fonts in question are called Sanskrit and New Sanskrit.
Please update the question to attach or link to a small sample document for others to test. It may depend on how the styles using these fonts are defined and whether font-fallback is occurring i.e., tdf#71603.
I do not have any knowledge of Sanskrit so forgive any language examples.
I do not have Windows and cannot test those versions. I am using LibO 5.1.1.3 EN_GB version on Linux-Mint-mate. I do not have the Sanskrit font installed but my system has Lohit Devanagari which comes with the system. Using the Insert Special Characters I can write फङङचबहथआ, excuse me that it does not make sense. Little squares showing instead of characters usually means that the font has no character defined for the character you have entered.
You could try the Lohit Devanagari font as I have to see whether there is a Font problem or if it is LibO or the system setup…Peter