Hi jake davies
Since you've already tested the controllers on multiple Xbox consoles and a PC and both exhibit the same behavior, that tends to point away from the Xbox console itself and away from a Windows driver issue. One thing that would help narrow this down is confirming the exact controller model and firmware version shown in the Xbox Accessories app.
If the issue began immediately after a firmware update and affects multiple controllers running the same firmware, please report it through the Xbox Accessories app or Xbox Support, as that may indicate a firmware-related issue rather than a hardware fault. Also, does the constant upward input appear in the Accessories app's thumb stick test screen, and if so, which stick (left or right) is showing the movement?