When I update.
Grav v1.6.31
Admin Plugins v1.9.19
then
Gantry Version: 5.4.36 / Released: October 16, 2020
There is a bug when going to Gantry 5 Layout editor
Please note; the layout dropdown selection was also dissapearing.
I found that this bug also present in Gantry 5.4.35