Update: Action Note 2.1
After receiving some user reports regarding a synchronization issue of the Action Center since the latest Windows 10 update, I had to publish just another update for Action Note.
After having a closer look, the reason of this problem was obvious, but not caused by the app itself. In one of the last updates, Microsoft enabled a new feature called Notification Mirroring, which synchronizes notifications across all devices using Cortana. Unfortunately, this was in conflict with Action Note's own cross-device online-sync feature.
The fix for this was actually easy: I was simply able to disable this mirroring feature for all Action Note notifications. Personally, I would suggest that Microsoft should not auto-enable this feature be default.
Beside that major fix, version 2.1 comes with a new alphabetical ordering option, which was requested by several users via email. Additionally, I updated the translations for the Polish and Swedish versions.