Whenever I launch the Notes app, it causes the Calendar app to launch as well. I am clueless as to what to try. Once the Notes app is open and I have quit the Calendar, everything seems to work fine. I use Notes a lot and this can be very frustrating. I have updated to High Sierra 10.13.5 since this has started but updating had no effect on the problem. Anyone know how to fix this? I'm running on an iMac.
You should check to see if there is a webcal URL in a note somewhere in Notes.app.
If there is, Notes will open Calendar.app and ask you to subscribe. If you don't actually want to subscribe to this calendar, just delete the webcal URL in the note (or delete the note entirely) and Calendar should not open again.