If you have the older 2009 version EF-S 28-135mm and can manually focus the lens at focal lengths between 100mm and 135mm, but autofocus does not work beyond 100mm it's probably due to a worn ribbon cable inside the lens that connects the main PC board near the back of the lens with the focusing elements in the extending part of the lens.
As the lens extends for longer focal lengths the connecting flex cable is unfolded. Sometimes those cables wear to the point as it unfolds there is a break in continuity along one or more of the traces inside the ribbon cable. This is not that uncommon a problem among lenses with extending barrels and focusing elements in the part of the lens that extends.
Trying to replace a flex yourself without knowing your way inside a modern lens is like trying to disarm a land mine without understanding how they are put together inside. You're just going to end up with a big mess. Having the lens professionally repaired will probably cost more than the lens is worth, which is also more than you could buy another used copy of the lens. Your best two options are to either look for another lens or work around the issue with your current lens. Just be aware that if it is a worn flex cable, it's only going to get worse as the cable continues to tear and other traces begin to have continuity breaks in certain positions.
Manual focus (to infinity) is also not working beyond 100mm focal length, but it - and auto focus- does work when focused on objects within 10 meters. For focal less than 100mm, it works normally at both manual/auto at shorter distances as well as at infinity.
The original 2009 EF-S 18-135mm f/3.5-5.6 IS had a micro-motor autofocusing mechanism. AF should always be disengaged before attempting to manually focus any micro-motor lens. Not disengaging autofocus by sliding the AF/MF switch to MF (manual focus) before turning the manual focus ring can damage the lens focusing mechanism. It's possible the gearing has been stripped or the focusing mechanism otherwise damaged in a way that only affects it when the lens is zoomed to 100mm or longer.
The STM and nano-USM versions are "focus-by-wire", even in manual focus. There's no mechanical connection between the focusing ring on the barrel of the lens and the focus elements. When you turn the focusing ring on the lens it sends an electronic signal to the camera, which then sends an electronic signal to the focusing element in the lens to move. So even with manual focus, if a flex cable is the issue, it would cause manual focus as well as autofocus to not work when the cable is stretched to a position where there is a discontinuity in one or more of the tracings on the flex cable.