Hi Robert,
tables respond to the data you have in them – this is possibly why it’s different with more users. If one record on a page has wider data that on a previous page, depending on what your theme’s table css says, the table may overflow.
Since you determine the number of columns and the type of data in them and thus how wide the table needs to be and since every theme has a different page width, the plugin cannot offer a 100% safe css solution for all situations.
It sounds like you need to adjust the css to your theme. Possibly setting a max table width ? You may also want to tailor column widths, maybe add some css to make the table responsive. The plugin html offers lots of selectors to give you max flexibility.
You may also want to add an opaque background to the table css to make it more visible if you are going to let it overflow. Some folks would rather the table overflowed, than that it gets squashed.
Some posts that may help:
https://wpusersplugin.com/3299/amr-users-css-html-and-styling/
https://wpusersplugin.com/3789/adding-custom-css-to-a-wordpress-website-for-plugin-html/
see tips on coping with a wide table:
https://icalevents.com/2685-long-urls-in-event-content/