Reminder emails are malfunctioning

[druXter]

Reminder emails are being sent twice, and the "Time Before an Appointment" field can no longer be edited. Error message: "Settings cannot be applied." (Translated from German)
Version 2.7.4

[SergeyMosin]

I am trying to replicate this but no luck sofar. Did you update from an older Appointments version or was it a fresh install. Also, if possible can you send me ( sergey [at] srgdev.com ) the setting dump ( Settings (for the malfunctioning page) > Advanced > Debugging > Settings Dump )