If I had to guess I'd say cooling. What filament are you using, what print temp, and what fan speed? And more importantly where is the printer?
Creality makes a little tent for the Ender 3 and it helped with a lot of inconsistent prints I was getting. In winter time the printer was in a super cold room and bigger prints would warp. But just normal airflow in a room can cause enough of a temp difference to warp big prints like that. If you can shield the sides of your printer with something that might help.
Hello netizens of Lemmy, while printing this single wall wing segment i ran into a problem with significant bulging around the middle. This causes the segments to not fit onto the frame or each other. If anyone has ideas on how to fix this, please share. At this point i'm pretty desperate and willing to try just about anything.