I use the Reman Covariant Shield on my Excelsior Retrofit. By default, I keep the Reman visuals on. When I unequip an impulse engine and equip a new one (such as, swapping between the Breen combat impulse engines and the Borg assimilated subtranswarp engines), the Reman visuals on my ship will turn off. I have to Disable Visuals by right-clicking the array and then re-enable them to get them to appear. I believe this happens in system space as well. Not sure if this happens with any other ships yet.
The square background behind my ship's avatar in the Status screen will turn white at the same time.
Ticket ID #1,238,766.
EDIT: The Reman visuals will reappear when I zone into a system. I confirmed the visuals will disable again if I swap impulse engines in system space too.
This is what happens: I switch from the Breen engines to the Borg engines in sector space, and the Reman visuals will auto-disable. I zone into a system, and they will be re-enabled when my Excelsior-R warps in. I switch back to the Breen engines from the Borg engines in system space, and the Reman visuals auto-disable again.