Importing photos into app

Using an iPad Pro, have been attempting to import photos into a third-party app called Procreate.

Here's what happens:only twenty or so photos from my 1300-image Photos library appear. Have played with the iCloud settings, but nothing makes any difference:

the same few photos appear, along with hundreds of empty files identified only by numbers.

The Procreate forum advises me to make sure my iCloud settings are correct. No combination appears to help.

Thanks in advance for advice to an idiot.