Why are permissions on new directories different between 16.04 and 20.04?

I've just migrated a system from Ubuntu 16.04 to Ubuntu 20.04. This system runs a set of scripts that create new directories as part of their normal operation. On both systems, the parent/ directory is owned by the same user and has the same permissions (drwxr-xr-x). On the Ubuntu 16.04 system, the script-created subdirectories parent/subdir1/ have the same permissions as parent/, drwxr-xr-x. On the Ubuntu 20.04 system, these subdirectories are instead created with permissions drwxr-x---. The scripts have not changed between the two systems, yet the subdirectories they create have different sets of permissions.

Question 1: Between Ubuntu 16.04 and 20.04, did something change about how default permissions are determined for a newly-created subdirectory?

One potential complication to this question is that the new subdirectories are being created in an external NFS partition. That is, the parent/ directory lives on this NFS partition, so it's literally the same directory for both Ubuntu systems. Both Ubuntu systems are ext4, and they mount this partition via identical systemd unit files.

Question 2: Between Ubuntu 16.04 and 20.04, did something change about how the ext filesystem interacts with a mounted NFS filesystem, particularly for the purposes of creating files and folders?

In addition to these questions, I'm also open to other suggestions about why my new directories have different permissions after the migration.