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The devices that show connected, but no internet connection, are they connected via WiFi or Wired connection?
If via WiFi, are they connected to the 2.4GHz or 5GHz band network?
In case it is via WiFi, be advised that it is prone to signal interference, which may cause dropouts, slow speed, etc.
We've some articles that will help you improve your home WiFi network.
Let us know how it goes.