There might be some interference with other 2.4GHz devices, such as your mobile or portable computer, which are connected to your home WiFi network and are located very close to the parent unit.
In order to avoid such interference issues, it is always recommended to keep such devices at least 5 feet away from the monitor. In many cases it is even enough to move your mobile device about 8-10 inches away from the monitor and this should solve the problem. If the monitor has an antenna, please ensure it is raised as it assist with signal strength
Also, please take into account that objects that block line-of-sight between the transmitter (camera) and the receiver (Parent Unit), may reduce the range. Such objects could be: any large metal object, like metallic doors or reinforced concrete between the baby and parent unit.
The signal strength may also be reduced by other solid structures, like walls, or by radio or electrical equipment, such as cordless or mobile phones, TVs, computers or dimmer switches. In order to minimize the environmental influences, it is recommended to keep the baby monitor (baby and parent units) at least 5ft away from these types of products.