fix vercel#494

src/use-swr.ts

@@ -315,8 +315,9 @@ function useSWR<Data = any, Error = any>(
         shouldUpdateState = true
       }
     }
+
     if (shouldUpdateState || config.suspense) {
-      if (unmountedRef.current) return
+      if (unmountedRef.current || !firstMountedRef.current) return
       rerender({})
     }
   }, [])
@@ -325,6 +326,8 @@ function useSWR<Data = any, Error = any>(
   const unmountedRef = useRef(false)
   const keyRef = useRef(key)
 
+  const firstMountedRef = useRef(false)
+
   // do unmount check for callbacks
   const eventsRef = useRef({
     emit: (event, ...params) => {
@@ -536,6 +539,8 @@ function useSWR<Data = any, Error = any>(
     // after `key` updates, we need to mark it as mounted
     unmountedRef.current = false
 
+    firstMountedRef.current = true
+
     // after the component is mounted (hydrated),
     // we need to update the data from the cache
     // and trigger a revalidation