Hi,
Have you checked the your "pre-owned" HXFX is running the latest firmware v.3.71 ? If not, it is strongly recommended that you update, as it not only does it contain extra /new effects, but also many unlisted bug fixes.
If it is already on v.3.71, then the usual approach to when things don't appear to be functioning correctly is to perform a Factory Reset to clear out any possible glitches.
To reset your unit make a backup of the contents of your HXFX using HX Edit v.3.70, then while turning on the power, hold down FS6 & Tap. When it is fully reset you can then restore all your stuff from the backup you made earlier, and it should go a process of rebuilding the presets. This is normal and it is done to upgrade all your presets to the latest format.
Hope this help/ makes sense.