DIAGNOSIS This is usually a conflict with your router's DHCP lease time or an IP address conflict. The printer gets a temporary IP from your router, loses it, and can't find its way back onto the network.
FIX Log into your router's admin page. Find the list of connected DHCP clients (often called 'Attached Devices' or 'DHCP Reservations'). Locate your Brother printer and assign it a static IP address or a DHCP reservation. This ties the printer's MAC address to a specific IP on your network so it never changes. You'll need to re-configure the printer's wireless connection once with this new fixed IP info.
IF THAT DIDN'T WORK The printer's wireless hardware might be going into a deep sleep. On the printer's control panel, navigate to Network > WLAN > Setup > Advanced Setup. Look for a power-saving or sleep setting related to the network and try disabling it, so the wireless radio stays active.
HEADS UP If you're using a mesh Wi-Fi system (like Google Wifi, Eero, etc.), ensure the printer is connected to the main router node, not a satellite. Some satellites have issues maintaining connections with older wireless devices like printers.