Add check for asyncio event loop to remain the same

telethon/client/users.py

@@ -30,6 +30,10 @@ class UserMethods:
         return await self._call(self._sender, request, ordered=ordered)
 
     async def _call(self: 'TelegramClient', sender, request, ordered=False, flood_sleep_threshold=None):
+        if self._loop is not None and self._loop != helpers.get_running_loop():
+            raise RuntimeError('The asyncio event loop must not change after connection (see the FAQ for details)')
+        # if the loop is None it will fail with a connection error later on
+
         if flood_sleep_threshold is None:
             flood_sleep_threshold = self.flood_sleep_threshold
         requests = (request if utils.is_list_like(request) else (request,))