try

rollup.config.js

@@ -135,7 +135,7 @@ function generateDepFile({ outputFile, sourceFiles = [], configFiles = [] }) {
   let timestamp = Date.now();
 
   // Save the depfile just before the node process exits.
-  process.on("beforeExit", () =>
+  process.once("beforeExit", () =>
     writeDepFile({ outputFile, sourceFiles, configFiles, timestamp })
   );
 
@@ -160,7 +160,7 @@ function writeDepFile({ outputFile, sourceFiles, configFiles, timestamp }) {
   const outputDir = path.dirname(outputFile);
 
   // Assert that the discovered bundle inputs are files that exist on disk.
-  sourceFiles.forEach(fs.accessSync);
+  sourceFiles.forEach(f => fs.accessSync(f));
   // Since we also want to rebuild the bundle if rollup configuration or the the
   // tooling changes (e.g. when typescript is updated), add the currently loaded
   // node.js modules to the list of dependencies.