Youtube gives you a 1280×720 pixel window out of your 360 Video.
When you are working with titles in Adobe Premiere you have to know, where to put the titles and words or lower thirds, to be visible.
Just create a 1280×720 color matte and place it on top of your video timeline.
Lower the opacity to 50% or as desired.
The Mask/Matte/Window will be in the middle of the image.
This will be the visible part of your 360 Video on Youtube.
You can place your titles and lower thirds in this frame and it will be visible.
Titles in 360 Videos look great! You just have to know where to put them!