package scala-2.10.6-16.fc31.noarch is filtered out by modular filtering

[Norman Gaywood]

After updating a Fedora 30 system to 31, I can't install scala:
# dnf module list scala
Last metadata expiration check: 0:31:21 ago on Mon 06 Jan 2020 13:31:04
AEDT.
@modulefailsafe
Name                       Stream                        Profiles
           Summary

scala                      2.10 [e]                      default
            A hybrid functional/object-oriented language for the JVM

Hint: [d]efault, [e]nabled, [x]disabled, [i]nstalled
# dnf install scala
Last metadata expiration check: 0:31:32 ago on Mon 06 Jan 2020 13:31:04
AEDT.
All matches were filtered out by modular filtering for argument: scala
Error: Unable to find a match: scala

If I try to install a package that depends on scala:
 # dnf install ant-scala
Last metadata expiration check: 0:32:13 ago on Mon 06 Jan 2020 13:31:04
AEDT.
Error:
 Problem: package ant-scala-2.10.6-16.fc31.noarch requires scala =
2.10.6-16.fc31, but none of the providers can be installed
  - conflicting requests
  - package scala-2.10.6-16.fc31.noarch is filtered out by modular filtering
(try to add '--skip-broken' to skip uninstallable packages)

How can I find out why scalar is being "filtered out by modular filtering"?

This is an updated fc30->fc31 system. A clean install of fc31 will install
scala OK.