calendar notifications not always occurring

[Angry_Subscriber_8472]

I'm using the default calendar app on my Verizon Galaxy S5 and I've had several occasions recently (past month) where either the calendar notification I had scheduled did not announce ("fire off") or was significantly later than the time I had it scheduled for.  Today I had a 12 noon meeting that the notification finally occurred 40+ minutes after the event.  I've checked that it appears to be synced with my Google calendar and settings of the calendar app only had the Hide declined events was checked which I've now unchecked, now only Vibration is checked, with "bar notifications" alert type selected and notification sound set to "On Time".  I've also had events (like last Friday) that I never received a notification for.  I've checked for updates and I'm up-to-date and last reboot was Sept. 13 2017 @ approx. 11:32AM (CDT)  I've also looked at the sound and notification settings and all are above the mute setting (notifications is set to max since last Friday when I had that one that didn't "fire" then)  I've got Notifications on lock screen set to show content and Notification access set to Applications cannot read notifications (which may be the problem?)

I've also had announcements that do fire on time, most recently yesterday (Tuesday) so this problem appears to be intermittent or coincident with another app.  Other apps I'm running are Play Music app (again system default one) Firefox browser, Contacts and Message+ (default messaging app)

Any guesses on why I don't seem to be getting calendar appointment announcements reliably?

Calendar app version: 2.1.36

Model: SM-G900V

HW version: G900V.05

Android version: 6.0.1

Kernel version: 3.4.0 (Aug 23 2017)

Build #: MMB29M.G900VVRU2DQH2

Config Version: J13.SAM.SMG900V.1

[bearone21]

if you use the google calendar it will sync.