I found these in the The Lion Guard Wiki page It's fun to compare early storyboard content with the final version, and there seems to be a few interesting changes made in some scenes.
The Lion Guard Main Title Sequence
The intro is pretty much the same as in the final thing, except that here after Rafiki's painting of Kion, we see him standing on Pride Rock with both his parents on the sides and Mufasa on the clouds. This scene was taken out and later repurposed in promotional material. Also, at the end we see an earlier version of the TLG logo, with a big pawprint behind the text.
Kion's Lament (Reprise)
Pretty much the same as the final version, except that Kion glances down at his reflection in the pond as he walks.
Tonight We Strike
There are two early versions of this song's sequence. The first one has many differences you'll notice, while the second one is almost all the same as the final. But most notably is that both have different endings. In the first one Janja and the hyenas are in a canyon/like structure with ledges, and in the second one all the hyenas form a pyramid formation with Janja at the top (I'm glad they didn't go with this one, hehe)
Ending Credits Sequence + Post-Credits Deleted Scene
Right before the end credits roll with the paintings, there was a scene with Kion and the Guard walking towards the camera. This scene was changed in the final version, but it was repurposed for the first teaser of Return of the Roar.
The credits sequence is pretty much the same with a few minor differences, but after it's over there was going to be an extra post-credits scene! It's pretty funny xD too bad they opted to take it out, but at least they still used part of it for, again, promotional material.
That's all there was. But I hope they'll reveal more of these in the future, it'd be great to check them out