DIAGNOSIS This is usually a power management setting conflicting with your network's router. The printer's 'Deep Sleep' or 'Auto-Off' mode is too aggressive and severs its network connection to save power.
FIX On the printer's touchscreen, tap Settings (the gear icon). Go to 'Preferences' > 'Sleep Mode' or 'Auto-Off'. Change this setting to 'Never' or to the maximum time available. Also, check for a separate 'Deep Sleep' setting in the same menu and disable it. This will keep the printer's network chip active and ready to receive jobs.
IF THAT DIDN'T WORK The issue might be with your router's configuration, not the printer. Some routers aggressively drop connections from devices they deem 'idle'. Try assigning a static IP address to your printer in your router's settings, as this can sometimes prevent it from being culled from the network list.
HEADS UP Turning off sleep mode will use more power—the printer will stay in a 'ready' state. It's a trade-off between convenience and energy use. If you print infrequently, you might just have to accept walking over to tap the screen to wake it before sending a job.