An infinite creation of slots gets created resulting into timeout and freeze the session/page when adding Repeated slots and saving setting "Divide into Slots?" = "No".

Environment setup:

moodle: 3.7.4+ (Build: 20200214)
mod_scheduler: 2018112602 (latest version for 3.5) Release date: Saturday, June 8, 2019, 3:19 AM

1. Create a course.
2. Enrol 1 teacher and 2 students.
3. Turn editing on.
4. Add a mod_scheduler activity, use default settings and save.
5. Go to the mod_scheduler activity and click "Add slots" / "Add repeated slots".
6. In the settings, change "Divide into slots?" to "No".
7. Leave all settings/values to its default, and click "Save changes".
Results:

• The browser will continue to process and load the request and will result into infinite, until it consumes resources to time out. At some point, you may need to stop/start your webserver.
• Log out and lot in again. Visit back the mod scheduler activity and you will see hundreds if not thousands of slots created.

This has been reported/replicated as well using:
moodle: 3.5.9+ (Build: 20191122)
mod_scheduler: 2017051402