I have not found this to be the case in my use of Finale v25. I do not use Win10, but I'm skeptical that it is the source of your problem.

If you have copied any passages with lyrics, check to be sure you are not altering the style of a different instance of the word(s) you want to change. One test you can try (on a copy of your file, if you wish) would be to Select All of the lyrics and try making a change (style, font size) to see if your lyrics change (and persist) on the page.

And, to state the obvious, make sure you save your file before exiting. (I'm sure you do, but just in case.)

Similar problem.  Copied lyrics don't seem to be able to retain multiple fonts.  There also seems to be no way to force a correction.

Any thoughts?

… Copied lyrics don't seem to be able to retain multiple fonts.  There also seems to be no way to force a correction …

Have you tried making the correction in the window Edit Lyrics?

That seems to work for me.

It also works for me in the Windows version of Finale.

Here is the problem :  choral piece, 2 verses, 2nd verse in different font.   Use SelectionTool with filter to select text only, copy text from one measure to another,.  Result: both verses have the same font now and it can't be changed.  I've tried several ways to fix the problem by deleting and reentering portions of the lyrics, but some of the font problem always remains somewhere.  Strange problem.  

In my experience, more time is lost by copying lyrics, whether by copying or cloning, than simply re-entering them.

>more time is lost by copying lyrics, whether by copying or cloning, than simply re-entering them.<

I'm sure that the Lyrics Tool saves time for someone but never me. Direct Entry has always just worked.

The Lyrics box can often be very useful in simple situations.  Cloning lyrics has cost me a lot of time.  It could be useful if we could learn exactly how it worked.  Cloning is convenient but dangerous.

I was able to fix my font problem by using the delete key (not backspace or erasing in the Lyrics Box) and then reentering using "Type into Score".

Thanks for the comments.

Cloning is not the same as copy and paste. No wonder you couldn't change one without changing the other. If you want to learn how the lyric box works, look here.

https://usermanuals.finalemusic.com/FinaleWin/Content/Finale/EDITLYRC.htm?Highlight=copy%20lyrics