I saw your issue on GitHub today. So I thought maybe I should recommend you AGS because Escoria is not stable enough. Then I saw your profile and found that you have AGS fork and now I found this post.
Godot is great engine but escoria framework is unstable. Escoria has five branches and one is named escoria-rewrite that tells me that people are not happy with other branches. Today I tested different combinations
Godot 2.1.6 with 2.1 branch
3.0.6 with 3.0, master, escoria-rewrite
3.1.1 with 3.1, master, escoria-rewrite
Now Godot community is working on Vulkan port which is good but who knows what will happen then escoria-rerewrite. I am also tired.
PS: I love Godot engine but escoria
Edit: Try Godot 3.1.1 with 3.1 branch
Edit: I found a way to fix your GitHub issue.
Open player.tscn
click on animation player node (default)
create walk_left and idle_left with flip_h checked then
open player_anims.gd and change
"walk_right", -1 to "walk_left", 1 and
"idle_right", -1 to "idle_right", 1
By doing this instead using mirror of walk_right and idle_right we are using walk_left and idle_left.
Any question feel free to ask
Godot is great engine but escoria framework is unstable. Escoria has five branches and one is named escoria-rewrite that tells me that people are not happy with other branches. Today I tested different combinations
Godot 2.1.6 with 2.1 branch
3.0.6 with 3.0, master, escoria-rewrite
3.1.1 with 3.1, master, escoria-rewrite
Now Godot community is working on Vulkan port which is good but who knows what will happen then escoria-rerewrite. I am also tired.
PS: I love Godot engine but escoria
Edit: Try Godot 3.1.1 with 3.1 branch
Edit: I found a way to fix your GitHub issue.
Open player.tscn
click on animation player node (default)
create walk_left and idle_left with flip_h checked then
open player_anims.gd and change
"walk_right", -1 to "walk_left", 1 and
"idle_right", -1 to "idle_right", 1
By doing this instead using mirror of walk_right and idle_right we are using walk_left and idle_left.
Any question feel free to ask