The interior flickering looks a like typical UHD Cache issue. Since there aren’t many moving objects or lights in this animation (or the movement is subtle, not affecting the scene lighting very much), the solution I would recommend here would be using the “load from file” option of the UHD Cache and just loading a single cache for each animation frame, on all computers taking part in the rendering. For more information, see: https://coronarenderer.freshdesk.com/support/solutions/articles/5000515648
The weird thing here is that with the “animation” preset, this kind of flickering should not appear at all. If you need some further help with this, or if you are interested in learning why it is happening, the best solution would be sending the scene to us (or some kind of simplified version of it) - Chaos