I got a 32" CHG70 with somewhat same issue. Mostly when i turn it on from very cold. Like overnight at an open window with close to frost temperature outside. It boots up with lines flickering at the bottom. Leaving it to heat up. Maybe preheat it b4 throwing a signal at it fixes the issue. Guidelines to testers testing monitors like this, is to allow them to heat up first. That and extreme cold was my issue. (Sounds like 1980’s monitors, but im not kidding ^^) Ofc there are many other culprits to consider as earlier answers have stated.