I have everything set how it is in the default theme, yet whenever I hide the widget with an animation and reshow it, the animation plays without unhiding the widget. To be clear, it shows the widget with the animation on the first button press - after that, it just plays the animation without showing the widget.

Here's how everything looks in the editor:

Showing
Button: Restart storyboard "SB_ScoringBox_In" on condition "C_ScoringBox"
Storyboard: Show widget "W_ScoringBox", play animation "A_ScoringBox_In", set condition flag "C_ScoringBox" (all in same item)

Hiding
Button: Restart storyboard "SB_ScoringBox_Out"
Storyboard: Play animation "A_ScoringBox_Out", unset condition flag "C_ScoringBox" --NEXT ITEM-> Hide widget "W_ScoringBox"

Condition Flag Settings
"visibility" is UNCHECKED
Everything else default

Animation Settings
"reset to default" is UNCHECKED
Everything else default

Really not sure what's happening, any help is appreciated!

It sounds like your condition for Show is to have the C_ScoringBox "set". But when you run the Hide sequence, the C_ScoringBox is unset. Then the condition fails the next time you want to Show.

I think the Show action Restart storyboard should have C_ScoringBox as condition selected, but with the box unchecked (meaning: this condition must be in the "unset" state to run that action).

Seems to be a glitch with the "ScaleX" animation. I changed all the condition flag stuff around and it still wasn't working - but after switching from "ScaleX" to "Opacity" in the animation, it worked perfectly.

That's strange... Any other animations that you have this issue with? Is it just Opacity that works?

Just tried them all and Opacity is the only one that worked how it should

I always have this problem, you can solve it with put a value in Showwidget. The value is to change opacity from 0 to 1 in milliseconds.
if you use Hide or opacity in animation, only show do nothing.

Emmanuel's solution did indeed work, thank you!

Glad you found a work around. I can verify this issue exists, even when just using a simple fade out via the control button properties in the theme.

Thanks, I will look into this.

Sorry, I cannot reproduce your issue... What am I missing?

See here a very simple example that shows/hides a widget with a ScaleX animation, and a condition flag that ensures you cannot show it again when it's already visible and vice versa:
Link