When User Role Editor meets other CSS or JS was running endless in Select Role and changes its capabilities
Affected by CSS or JS in custom function() meets other CSS or JS
That conflicting CSS/JS should not be loaded to the URE’s own page. That is some code loads it globally, not only to page(s) where that CSS/JS is really needed. Can you identify, what plugin/theme loads it? If you load such CSS yourself, try to limit pages, where it’s loaded.