Hi @Doombar, sorry to hear about this.
Have you tried clearing the data for the app in charge of the alarms in the phone? By doing this, you will reset all settings for the app which might do the trick. In order to do this, find and tap Settings > Apps & notifications > Show all XX apps > Clock > Storage > Clear data > Tap "OK" > Restart the phone. Please note that this measure will also erase any reoccurring alarms, so you will have to set them once again after the restart if you have any.
Another thing that you can try is to reboot your phone in safe mode and set an alarm there to see if the behaviour persists while the phone is in safe mode. All apps downloaded from Play Store is temporarily deactivated while in safe mode and by doing this, you can see if this behaviour is caused by a downloaded app. For more information on safe mode and how to use it, click here.
Try these measures and feel free to keep me posted with the results!
