Those letters on that type fabric will be a problem no matter what you do...but
try doubling up on the backing 2 layers,
use solvy if you have it.
The best fix would be to change the text to a micro block style, those super thin columns will always dive into the fabric. You have to understand that you are trying to lay a thread between two needle holes that are most likely intersecting each other. The result is the thread has nothing or very little to rest upon so it either dives in or disappears all together.
I think you are chasing a ghost on this .
mooseman