I have figured out the issue! There was a typo in the menu’s link to the calendar page. When that menu tab was clicked, it would redirect to the calendar, but the calendar wouldn’t change to the next month. Then, when I manually retyped the URL into the “Custom Link” option for creating my menu tab, it started functioning! Before I typed it in, I had gone to “Events>>Settings” from my dashboard, then clicked on the “Where’s my calendar? Right here.” link and copied and pasted that URL.
When I typed it in manually, it worked and has been working ever since. So, there was something wrong with the location the Settings took me to when I clicked “Right here.” No idea what happens behind that link, but my issue has been resolved and I now have a functioning calendar. 😀