Bash Alt+Arrow keyboard combination not working in Terminal under Mojave
Can you check:

Go to Terminal > Preferences... > Profiles > Keyboard

From this pannel, check those two lines:

Key = Alt+← Action = \033b

Key = Alt+→ Action = \033f



They might have gone away so you may create them again, or edit and double check the key, the modifier, and the action associated:





As a workaround, (actually it could even be better, so that you don't need to reach for the arrow keys), you could use Esc+f (jump forward) and Esc+b (jump backward).

And because the Esc key is far to reach, for more convenience, map the Caps key to Esc key with Karabiner Elements.

So that you can jump back and forth with Caps+f and Caps+b.