How to solve this issue?
By refreshing the reminders app on your mac:
Just quit Reminders.app on your mac, run Terminal.app and run this command:
defaults write com.apple.reminders RemindersDebugMenu -boolean true
Open Reminders.app again and now when you click Command+R -> it will refresh :)
Hope it helps you with syncing your reminders list between your mac and your iPhone or iPad