I've moved this thread to Plugin support. Please be sure to post your threads in the correct forum next time. Thank you.
Yanfly's plugins are stable - if such errors appear that is always due to one of the following mistakes made by you:
1) you installed some of the plugins in the wrong order - there is a reason why Yanfly posted the suggested order on his website, a lot of things can go wrong if you use a different order in the plugin manager. You can skip plugins you don't need in that order, but you can't add something at the wrong position.
Drag'n Drop the plugins in your plugin manager until they are of the correct order
2) you installed a plugin that makes old savefiles incompatible (about 80% of them do) and forgot to start a new game.
Simply start a new game when playtesting and forget about all your saved files, you need to start traveling from the beginning again.
3) One of the plugins is not correctly configured
You cannot simply add a plugin and then ignore it - after each added plugin, check if the plugin properties are set correctly for your project, and if all notetags in the editor are without typos and where they're needed.
4) you installed additional non-yanfly plugins and those are either in the wrong order or generally incompatible.
You'll need to find out which two plugins are causing the effect, a good start for that would be a screenshot of the console output of the error message you described above.