Apps Script: Too many simultaneous invocations: Spreadsheets

This exception means too many executions were calling the same service, typically the Spreadsheet service, at the same time. It is a concurrency limit, separate from daily quotas and from the 6-minute runtime limit.

Google's quotas page lists 30 simultaneous executions per user and 1,000 per script. In practice the Spreadsheets variant shows up intermittently on triggered scripts, form-submit handlers and web apps when several runs overlap and all read or write the same spreadsheet.

Nothing is wrong with the code's logic; the same function succeeds when it runs alone. The fix is to stop overlapping runs from colliding.

function onFormSubmit(e) {
  const lock = LockService.getScriptLock();
  lock.waitLock(30000);
  try {
    SpreadsheetApp.getActive().getSheetByName('Log').appendRow(e.values);
  } finally {
    lock.releaseLock();
  }
}

Any handler that can be triggered concurrently should take a script lock before writing shared data. Keep the locked section short, and process bursts asynchronously from a queue. Note that waitLock throws if it cannot get the lock in time, so handle that case too.