edschen
We addressed this issue in the latest build of the OAuth2 Plugin (quite some time ago - February 9, 2023). Upgrade to v1.18.1, download/install the latest build of the OAuth2 Plugin, delete the existing Token, get a new Token, and your issue should be resolved moving forward.
Be sure to reload the webserver and PHP-FPM (if you're running it) after adding the new Plugin PHAR file to clear any file cache. PHAR files are typically aggressively cached on the server so you must ensure you clear cache so it loads the new PHAR file. If you are using a hosting provider it'd be worth asking if they have any file caching enabled in your environment as hosting providers sometimes have their own additional layer of file caching that you need to clear as well.
Cheers.