Welcome to the forum!

I could be wrong, but it seems to me that Finale is following standard practice:

When the principal text requires a syllabic slur, use a solid slur.

Slurs exclusively for the alternative text are dashed.

Are you saying that the standard practice makes no sense?

I had to erase all of my lyrics and type them in again to get the "auto-slur" feature to work.
This evidently ASSUMES that all vocal music will be written hymn style, strophic, with one verse on top of the other.

Well, I wish I hadn't "upgraded" to this version of Finale.

I have been using Finale since 1992, and this is the first I have seen of this.
It makes no sense.

This is not a matter of "principal text" and "alternate text."
It is a matter of different sections of the song.
AGAIN, it ASSUMES the piece is strophic and set up like a hymn, with one verse on top of the other.

And evidently we have no power to set it up according to our needs.

I am not sure how to reproduce your problem.

Indeed some of the Finale plug-ins would be better with more options for the user.

Perhaps you should make a feature request about the plug-in Auto Slur Melismas.

Just be careful to explain the issue clearly, with an example - including exact steps to reproduce the example.

Why not enter the slurs yourself, rather than relying on an Automatic process that doesn't do what you want it to do?

I agree automatic is not always the best choice. Really doesn't matter if you are using Finale or most anything else in life sometimes automatic isn't the best way to go.

Perhaps you should make a feature request about the plug-in Auto Slur Melismas.

Good luck there!

https://usermanuals.finalemusic.com/FinaleWin/Content/Finale/pi-auto-slur-melismas.htm?Highlight=auto-slurs 

You don't have to run this plug-in but, when you do, it gives the exact behaviour that you are describing.

What it does

The Auto Slur Melismas plug-in scans a document for lyric syllables that carry over two or more pitches and adds slurs accordingly. This is a standard practice for notating melismas. After running this plug-in, melismas appear wherever there are word extensions or hyphenated syllables under note changes. After running the plug-in a message appears indicating the number of slurs that were added. Dashed slurs are added for any melisma that applies to subsequent verses (and not the first verse). Solid slurs are always used for the first verse.

As for myself, I've never used it but, if I did, it would be the first verse only. For hundreds of years, hymnals and song books have done without dashed slurs. Singers are never confused by their absence (none of the hymnals I use currently have them). Unfortunately, once Sibelius added this nonsense, everyone else had to have it, too. Like you, I believe that they look terrible and only serve to clutter the page.

So, technically, it's not a problem—it's working as it should—but a Feature Request: 

Please give us the option of disabling slurs in subsequent verses when using the 

Auto Slur Melismas Plug-in

Dashed slurs do have a traditional place:

a) in a critical edition to indicate editorial slurs and phrase markings not indicated by the composer.  

b) under tenuto and staccato notes in string parts to indicate that the bow does not change direction (even then, it's not really necessary as this Beethoven example shows) .