Turn mower off and remove its disabling device. Put on heavy gloves. Inspect drive and front wheel along with mowing blades for stuck or accumulated mulch, vines, rope, toys, small branches etc. Clean if needed then make sure wheels rotate freely and let the mower mow for a week to see is mowing duration improves. A health battery should give 1-2 hours of mowing (Depending on RK’s model).
If Step 1 was not the issue, make sure the blades are sharp, and mowing disc centered and not wobbly. If dull or wobbly replace mowing blades and disc, if needed, and monitor mowing duration.