Automatic Travis CI not automatically running for PR

I don’t understand how it works, but a repository for which I became the maintainer back in Dec 2019 always kicked off some tests every time a PR was entered. (It was set up that way before I took it over). The repository is GitHub - matplotlib/mplfinance: Financial Markets Data Visualization using Matplotlib

You can see example Travis CI runs here:

The problem is, sometime after June 6, 2021, when a PR kicked off this Travis CI run, new Pull Requests now do not kick off a Travis CI run. There are two PR’s since then: 416 and 417 … neither of these PR’s kicked off the expected Travis CI.

Since I don’t really understand how these were getting kicked off in the first place, I am at a loss to figure out what changed and why the CI is not getting kicked off for each new PR. Can anyone help me please? Thanks.