over the past weeks, I have uploaded some maintenance releases for Scheduler to the plugins database. These contain a collection of fixes that were already available from github earlier.
Release 2.7.2 - for Moodle 2.7 and 2.8.
Release 2.9.1 - for Moodle 2.9, 3.0 and the upcoming Moodle 3.1.
I am working on a separate Scheduler 3.1 release with some new features, but this will be available only later this year. Meanwhile, the 2.9 branch of Scheduler can be used on Moodle 3.1.