The possible reason for the warping of ABS could be the build platform is not leveled well. If there are big variations, eg >1mm difference. I would recommend leveling the build platform manually by adjusting the 4 knobs under the platform, until the 9-point auto-leveling compensation values are all within 0.5mm.
If you are printing ABS,You can also take following steps to enhance the adhesion between the prints and the build plate.
1. Make sure you close the wind door on the extruder, this will minimized the warpping of ABS.
2. In the UP BOX+ package, we also provide perforated build plate. This kind of build plate has much stronger adhesion than the flex board, we highly recommend using the "Perf board" to print large ABS objects.
3. Preheating build platform will help to reduce the warping.
4. Printing with raft will aslo be recommend to help adhesion.