Mac calendar not saving standard reminders/alerts

Hello there, Alex.

It seems like your alerts are not functioning as expected with a particular vendor's cloud-based calendar. It seems like you've done some great and extensive troubleshooting already but something you could try to pinpoint further wether it's OS related or specific to your Vendo'sr settings is test in another user account. The following Knowledge Base article offers up how to accomplish that:

How to test an issue in another user account on your Mac

Before trying another user account

If you're seeing unexpected behavior on your Mac try these steps first:

Try searching Apple's knowledge base for the specific symptom or alert message you're seeing. There might be simpler steps you can take to resolve the issue.

Try starting your Mac in Safe Mode. Restart your computer. Hold the Shift key when you hear the startup sound. Release the Shift key when you see the Apple logo appear. This starts your Mac in Safe Mode. Safe mode performs a directory check of your startup disk, and removes some cache data. After your Mac finishes starting up, restart your Mac normally (without holding the Shift key) and see if the issue is resolved.

Make sure your software is up to date. The issue you're seeing might be addressed by installing available updates.

Check to see where the issue happens. If an issue appears before you see your desktop, it's less likely that it's related to a user account or setting. If an issue happens with a website, see if pages from other websites load correctly first. There might be an issue with the site and not your Mac.

How to test with another user account

You can figure out if unexpected behavior is related to user file or setting by trying to reproduce the issue from another user account. This process includes creating a new user account, logging in to it, and testing for the issue.

Create a test user account

1. From the Apple menu, choose System Preferences.
2. Click the Users & Groups icon in the System Preferences window.
3. Click the lock icon, then enter an administrator name and password.
4. Click the Add button (+) below the list of users.
5. Choose a type of user from the New Account pop-up menu.
6. Give the user a full name, account name, and password.
7. Click OK.
8. Close the System Preferences window.

If there are documents from your original user account that you want to test with, place a copy of these items in the Shared folder in the Users folder. Press the Option key while dragging a file to this folder to create a copy.

Log in to the test user account

Log out of your current user account by choosing Log Out from the Apple menu, then log in to the new account you created. If you're prompted to sign in with your iCloud account or Apple ID when you log in, skip this step.

Try reproducing the issue

Try the same steps that caused the unexpected behavior to appear before. For example, if you were unable to print, try printing from this user account. If you were unable to connect to the Internet, try browsing a website from this user account.

If you were using any specific settings that testing depends on (such as using a specific email account or iCloud account) set up the same account in the test user. For email and most other settings you can use the Internet Accounts pane in System Preferences to set up these kinds of accounts. If files from your home folder are needed for testing, copy them to Shared folder in the Users folder (/Users/Shared). After logging in as the test user, copy these items to the same location in the test user's home folder to test with.

If an issue happens in only one user account

If performing the same steps in a test user account doesn't result in the same unexpected behavior, you most likely don't need to reinstall any apps or OS X.

• If an issue only happens in one app, check the app's documentation or support website for instructions on troubleshooting specific preference or setting files.
• If you need help with a specific alert message or issue, search the Apple Support website for the text of the alert message you're seeing.

If an issue happens in more than one user account

If the same unexpected behavior happens in more than one user account on your Mac, try checking for software or hardware issues.

Thanks for reaching out to Apple Support Communities.

Cheers.

Hello again, Alex.

Thank you for the follow up. Being that your iCloud and Google calendars are functioning as expected, even in the new user, but your other calendar service is not, then it looks like your mac is behaving normally and we’ve isolated it to this specific vendor’s calendar. At this point you may need to go back to the vendor to determine what settings/restriction the calendar may have that are not allowing you to customize it the way you would like.

Sincerely.