Can the save of a canva take too many ressources for a web server?

I'm creating an app that you can assimilate to an online shared paint. When my canva contains few shapes, the save on the server, the encoding and the decoding of this canva works 10/10 times. But when I want to use an image as background of this canva, it works about 1/10 times. The others times, the server doesn't save the encoding canva at all... The thing is that when I use my app in local, it's also OK even with an image.

Do you guys thinks that it's possible that saving this canva requires too many ressources for the server ? Thanks you