Instrument appears in 'Players' but not in 'Layouts' panel

I am working on an orchestral arrangement, and the first instrument – Flute – appears in the Players list on the left, but no in the Layouts list on the right. So when I select Engrave or Print, Flute is not an available choice. How can I fix this issue, as i want to have the arrangement formatted as perfectly as possible before saving this as a template.

You do this by adding a (flute) part layout:

For no known reason, I created a new Flute part Layout, but it kept disappearing. The only solution I found was to delete and re-add a Flute part, which seems to have worked so far.

Can you explain, where and how did it disappear?
Did it disappear in Setup Mode from the right panel?
Or did it disappear in Setup Mode from your players list on the left side?
Or did the newly created flute part layout show no music? This is the case when you create a new layout and don’t link it to a player on the left and to a flow at the bottom.

I created the new Layout and linked it to the Flute part. Later after writing in some string parts, I noticed that the Flute Player is still present but the Flute Layout had disappeared. As mentioned, when I deleted the Flute and added a new Flute Player, the Laout for Flute appeared and stayed.

This sounds like a bug.
How did you then proceed?
If you had already put music into your original flute instrument, you probably copied it over to the new flute player system?

yes, pasted it into a blank part then re-pasted it back into the new part

Do you have a stripped-down version of this project?
Just to make sure, you are avoiding unnecessary steps.
If you add a new player holding a flute, an intermittent blank part is not necessary.
Supposedly, your original flute and the new flute systems are next to each other in the full score.
You would only need to select the music from the original flute system and “Move to system below”.

Since there might be a corruption in the Flute part that was not properly linking to its Layout, I decided to delete it before adding a new one. Since Oboe was blank at the time it was no worry either way.