This is not uncommon but there are a number of possible causes. We need more information.

https://makemusic.zendesk.com/hc/en-us/community/posts/215729367-General-Discussion-House-Rules 

There have been many threads on this over the years—none involve a bug. Search for the actual symptoms to find them.

What is the source of the file. Are you creating a new file from scratch? Is it an old one you created? Did you download a file from the internet or was it sent to you?

Kathryn Hayward,

1) We need to know the steps you’ve already taken (to solve the problem), so that we can rule out things.

You mention some steps:

“I have tried clicking the down arrow to adjust the time stamp and it will still glitch and play back from a random time stamp (always the same number in a given file --- yes, I have tried to open multiple files and it still has issues; newer files, older files, you name it). I have also tried, manually entering 1|1|0000, hitting enter, and no success.”

Have you tried other steps?

Like e. g. resetting the Preferences?

2) A screen shot of your Playback Controls window might give us a clue.

Before taking the screen shot, please click the down arrow so that we can see the full, expanded window.

What happens if you select to playback from the leftmost measure? That's what I usually have set. At least that might be a workaround.

I'm also not sure if it's related or even macOS-specific, but there is a longstanding bug I've reported to MM in which you can't change the tempo in the Playback Settings and then select Reset or Use Current Settings in the playback settings expecting tempo to now playback at your chosen speed. It should ignore existing metronome markings in the score, but doesn't. This used to work perfectly.

If your settings are not responding to changes you are specifically enter into the time stamp, I wonder if it is a general Playback Settings issue similar to the one I described for tempo? This isn't a solution, of course, but does suggest a larger issue MM needs to address...finally.