by Matthew Davidson.
I know this is an older thread, but the solution to this issue is being debated now at https://moodle.org/mod/forum/discuss.php?d=273202
the code to fix this issue is on https://tracker.moodle.org/browse/MDL-47777
If you have a use case as to why it might be needed to allow more than 20 files, let Moodle know about it. Thanks!