DIAGNOSIS This is a classic sign of a dust blob on the internal 3LCD panels or the integrator optics. Dust has settled inside the optical block and is being projected, usually appearing as a soft, out-of-focus smudge, often yellowish.
FIX Use the built-in 'Dust Blob Removal' utility. Go to Menu > Settings > Maintenance > Dust Blob Removal and follow the on-screen instructions. The projector will run a specific pattern and attempt to vibrate the dust off the panels using its internal mechanisms. Run it 2-3 times. This solves the issue for many users.
IF THAT DIDN'T WORK The dust is likely stuck or on a surface the utility can't clean. For persistent blobs, the optical block needs professional cleaning by an Epson service technician. Do not attempt to open the optical block yourself—it's a sealed, precision-aligned unit.
HEADS UP Prevent this by always letting the projector run its full cooling cycle before unplugging it. Sudden power loss prevents the fan from running to seal the optics compartment. Also, avoid using the projector in excessively dusty environments.