The Special:AbuseFilter editing form appears to currently be unusable. The JS console reports:
load.php?lang=en&modules=jquery%2Coojs-ui-core%2Coojs-ui-widgets&skin=vector&version=1ah9t:158 Uncaught Error: Widget not found at Object.OO.ui.Element.static.unsafeInfuse (load.php?lang=en&modules=jquery%2Coojs-ui-core%2Coojs-ui-widgets&skin=vector&version=1ah9t:158) at Object.OO.ui.Element.static.infuse (load.php?lang=en&modules=jquery%2Coojs-ui-core%2Coojs-ui-widgets&skin=vector&version=1ah9t:158) at Object.OO.ui.infuse (load.php?lang=en&modules=jquery%2Coojs-ui-core%2Coojs-ui-widgets&skin=vector&version=1ah9t:154) at HTMLDocument.<anonymous> (<anonymous>:93:521) at mightThrow (load.php?lang=en&modules=jquery%2Coojs-ui-core%2Coojs-ui-widgets&skin=vector&version=1ah9t:48) at process (load.php?lang=en&modules=jquery%2Coojs-ui-core%2Coojs-ui-widgets&skin=vector&version=1ah9t:49)
I've observed this on group 0 and 1 wikis in safemode. Tested in Chromium 77 and Firefox 69 on Ubuntu.