The Fresco resets when editing the low trim or high trim settings. This is a known firmware issue with 108 firmware specifically (potentially 107 as well).
This may also occur on the setpoint screen or other screens with a large selection of options to configure.
The Trim settings and other settings can still be editing using Fresco Studio, this only impacts the touchscreen firmware.
Either edit the settings using Fresco Studio, or update to the latest version of firmware 109+.