The highest cut the RT can do is 60mm (2.4 inch). If the grass is substantially higher than this 60m, use a regular lawn mower and cut the grass to 60mm (2.4inch) height or lower. Now set the RT to its highest cut and let it mow for a week to cover the entire area.
Open Robomow App, check the Mowing Schedule: Increase the mowing days, working hours, duration, or number of mowing sessions per day as necessary. Wait a week and see whether the uncut patches are gone.
If issue remains: Contact Customer Support