Image upload fails

Upload limits are not the only thing that constrains your ability to upload and resize images. The most likely thing is your server is running out of memory to resize the image. If you are on shared hosting then even if your host says you have certain limits on your resources there is no guarantee these are actually available to you as they are shared between all sites on that hardware.

See this page for general "blank screen" troubleshooting: https://solutions.grabaperch.com/development/why-am-i-getting-a-blank-page