Animation bug - reversing halfway through

I have a problem with implementing a walk animation - the animation seems to stop halfway and reverse to the initial state, see here. All animations show fine in the preview window when importing from the FBX.

Here’s the transition, the preview window is show the animation correctly:

The animation state is below, the preview still shows the correct animation for all layers and the speed stays at 1 throughout.
The GameObject was plonked into this scene directly from the FBX with only an Animator component attached to the root. There’s probably something obvious, but I’m having no joy as of late.

Judging by the way your transition is setup, it looks like it’s permanently transitioning back and forth between your Idle and Walk states, could you share a screenshot of your animator, and the transition from Walk to Idle? Maybe the Walk condition is set to true in the put transition too?