Solution to what I had seen as a bug.

solid-repro/src/index.tsx

@@ -1,6 +1,6 @@
 /* @refresh reload */
 import { render } from 'solid-js/web';
-import type { Component } from 'solid-js';
+import { Component, createEffect, createSignal, onMount } from 'solid-js';
 
 import {
   Router,
@@ -10,15 +10,19 @@ import {
   useParams,
   useNavigate,
   hashIntegration,
+  useRouteData,
 } from '@solidjs/router';
 
 const Counter: Component = () => {
   const params = useParams();
-  const count = +params.count;
+  const [count, setCount] = createSignal(0);
+  createEffect(() => {
+    setCount(+params.count);
+  });
   const navigate = useNavigate();
   return (
     <>
-      <button onClick={() => navigate(`/counter/${count + 1}`)}>+1</button>
+      <button onClick={() => navigate(`/counter/${count() + 1}`)}>+1</button>
       <div>Count: {count}</div>
     </>
   );
@@ -32,10 +36,10 @@ const App: Component = () => {
     </Routes>
   );
 };
-
+// source={hashIntegration()}
 render(
   () => (
-    <Router source={hashIntegration()}>
+    <Router >
       <App />
     </Router>
   ),