Happy New Year. Sorry that you are stuck.
First, to the best of my knowledge there are NO ERRORS in the Game Schedules plugin. ERRORS stop program execution. So if that's happening, please send me a screenshot of the ERROR message and I will do my best to fix it.
I believe what you are seeing are NOTICES and WARNINGS. They do not stop, or even significantly impact, the program's execution. They are certainly NOT BUGS. You can witness the plugin working pretty well on my development site.
I believe your frustration is coming from these notices and warnings being printed on the front and back end (admin) displays. Understandable. So again, you can fix that by stopping the debug messages from printing to the screen. There are several ways
define('WP_DEBUG', false); might be changed or ignored but I can't debug every user's WP install or theme. If you follow the directions in the references I gave you above, you should be able to redirect the annoying messages from the screen to a file. It seems that will fix your problem. (If you would like some help doing that, please contact me at shoalsummitsolutions.com.)