And then look at the differences between the versions - there will be something in the change list in the release notes in AccelStepper.h file if something changed incompatibly.
BTW just looking at the code for AccelStepper 1.19 which I have shows an obvious bug in the constructor
which calls enableOutputs() at constructor-call time, which is not correct. This means the library will only
work for top-level constructors if called late enough in the initialization process, which is fragile to say the
least.
Constructors should never assume anything in the system is ready to use except the instance variables it
is initializing. Anything else should be done in a begin() method.
Bit of a surprize this, I've never seen AccelStepper fail, but it looks like that's luck - everyone calls
pinMode explicitly on the output pins anyway?