_process is called once per frame, and the crawl check is done with Input.is_action_just_pressed. That function will only return true when the action is pressed. If you hold the crawl button and _process gets called again, that same check will return false.
If I can make a suggestion, you should consider refactoring your code to make use of state machines. Unless your character only ever needs to run and crawl, you’ll likely have to add more if-statements to your code, and things will get messy quick. Using state machines will help avoid that problem. If you search the internet for something like “Godot character controller state machine”, you’ll likely find good examples.
On a separate note, it’s considered good practice to post your code as formatted text rather than as images, as this makes reading code much easier.