Ok, so it has to be a combination of plugins. Via your phpinfo() output, I discovered you’re using the same exact webhost, and php version that I am. I have mine at the defaults with 30 seconds, and 128MB memory, and I used the Simple Image Sizes plugin to register 16 total resizes on my site. Uploading a 1024×667 image and optimizing all the resizes took like 5 seconds, and finished without error.
So, the next step is a bit of a pain, but here is the only way I know of to find the ‘magic’ combination:
1. disable all plugins except EWWW, and upload an image. Does it work? If not, I’ll be really puzzled.
2. re-enable each plugin, one at a time, and upload an image each time. When it stops working, we’ve found the combination, and can try to figure out the solution.