OK, here's an odd one,
I have to make a couple of hard-coded language changes to the "The Events Calendar" so I keep a copy of it in a private repo on BitBucket. I use your wp.org override filter so it only looks to my copy for updates.

When using your "The Events Calendar Category Colors" plugin I get the 401 error on it that it cannot connect.

I mention this because it only appears to fail if "The Events Calendar" is in the override filter. When testing I tried other plugins such as "Event Tickets" and "WooCommerce" and everything worked fine.
The problem also only seems to appear after about a day, It does not occur immediately.
I hope that makes sense?
Can you install the support plugin. https://github.com/afragen/github-updater-support
It will install the WP Debugging plugin and ask you to install Query Monitor. QM will let you see any HTTP request errors. Those should provide more information.
OK, I'm getting a 401 Unauthorized error:
Which is odd, because when I first set it up the category colors does look at the WordPress repository (has WP logo next to it).
What鈥檚 odd is that I can put that URL into a browser and it works fine. Can you screenshot the QM error?
It seems the issue is with your override of The Events Calendar. Can you share the code you use in your override filter.
Was this previously working correctly? I may need access to your version of TEC to test.
Sure thing. Here's the filter:
add_filter( 'github_updater_override_dot_org', function() {
return [
'event-tickets/event-tickets.php',
'the-events-calendar/the-events-calendar.php',
'woocommerce/woocommerce.php',
];
});

We've only used this combination for a few months, I don't recall it working correctly.
I added you to the repository. Here's the url:
https://bitbucket.org/mystudioengine/the-events-calendar
I鈥檒l take a look later today and see if I can replicate this.
Wow, this was a real edge case. @PthPndr let me know if it's fixed for you. I works for me.
Haha, I'm sure it was. It's been running for a day, all looks good. Thank you very much for taking care of this.
I fixed another related bug where I wasn't saving a proper response if no tags were present. It caused GHU to constantly send the API call looking for a good response.
https://github.com/afragen/github-updater/commit/1550833b6f5084ca2d9f4fa90a331baf10378adc
Yeah, that looks like it fixed the other problem I was seeing with all the front-end requests. Looks a lot better now.