DIAGNOSIS You're likely hitting the limits of the monitor's adaptive sync range or running into a mismatch with your GPU's frame output. The CQ27G2's FreeSync range is 48-144Hz, and issues below that floor are common.
FIX First, make sure you're using a DisplayPort cable (the one in the box is fine). In the monitor's OSD, go to Game Setting > FreeSync and ensure it's 'On'. Then, cap your in-game frame rate to 141 or 142 FPS using a tool like RTSS (RivaTuner Statistics Server). This keeps you comfortably within the active sync range and prevents the buffer from overrunning.
IF THAT DIDN'T WORK Try forcing the monitor's Overdrive setting (in Game Setting > Shadow Control) to 'Strong'. Sometimes the default 'Medium' can cause slight ghosting that looks like tearing. If you're on an NVIDIA card, also check that G-SYNC Compatible mode is enabled in the NVIDIA Control Panel under 'Set up G-SYNC'.
HEADS UP If you're using an HDMI cable, the FreeSync range is narrower (I think it's 48-120Hz on this model). For the full 144Hz with adaptive sync, DisplayPort is non-negotiable.