I have missed a number of meetings because of this same issue, and it has been happening for a better part of the past year. Finally got frustrated, and look for a solution, only to find out that it's an ongoing issue that Microsoft still hasn't fixed. It is all external meeting invites, when it is not from another Outlook/Microsoft Account - this is primarily Google, but does extend to when I manually import an event using an ical file as well. I have to manually set a reminder notice, otherwise I usually miss these meetings.
Please prioritize this bug fix, as its negatively effecting mine, and my company's professionalism.
Not sure if it makes any difference, but I'm using a Mac, and using the desktop app. I'm sure this same issue is happening across Windows and in-browser platforms as well.