Hi,
last update of agency theme did a complete override of my files/folders and my site broke!?
So using gpm for theme updates means a complete theme reinstall?
Using gpm for grav update means only relevant files are updated.
Theme updates with gpm are diffrent???
If you make modifications to the theme, then update that theme, then yes anything that makes up that theme will get updated. Just like any CMS, theme updates should be done with caution.
We strongly advise you to inherit a base theme rather than modifying the theme directly. This will let you make updates to the base/parent theme without it overwriting your modifications.
NOTE, that you should be able to use a custom.css file in a theme without worrying about that file getting overridden because it is not by default part of the base theme. However, there is currently a bug in GPM that is causing this file to get lost on updates. I will endeavor to find out what is causing this and fix it for the next Grav release.
Thanks.
And yes even my custom.css disappeared
Just lost all my custom templates and css file due to this. Oh well wasn’t that much work I guess.
Good way to encourage people to use inheritance though!
And backup 
Sorry about this, I do have it on my list to look at next week.