Like many users, I've found that after 2-3 years of trusty use, my Harmony 880's volume up/down button has started to fail. Apparently the contacts and plastic nub under the Volume Up button finally broke. If I press it really hard, sometimes it responds, but usually either button causes it to change the volume lower. Rather than buy a new remote, I found this relatively simple workaround.
I rarely use these large Up/Down option buttons below the directional pad.
I went into each Activity in the Logitech Harmony Remote Software and chose the Customize Buttons option. Then I looked at the default volume control settings for the activity and copied those onto the large buttons as well. Like this:
Now the large buttons are working fine to control volume, and I’ve actually found them to be more comfortable for this purpose. If you still need somewhere to put those functions, assign them to a function on the LCD screen instead.