A quick way to find out the culprit (plugin or theme that is causing the issue) is to switch to the default WordPress theme and start deactivating the suspected plugins(keep checking the page after you deactivate the plugin).
Once you identify the plugin that’s causing the issue you can dive into the code of that plugin and see why it’s doing it or maybe contact the plugin author to take a look at it.
Let me know if you are still having issue with this.