lripmo

Hi t-p
Thanks for your reply.
I went through the troubleshooting list including help from my hostingprovider purging varnish cache.
Turning on Script debugging didnt help, but provided an extra error whenever i pressed a button on the keyboard while testing the post-editor:

printWarning @ react-dom.js?ver=16.13.1:82
error @ react-dom.js?ver=16.13.1:54
flushDiscreteUpdates @ react-dom.js?ver=16.13.1:21952
flushDiscreteUpdatesIfNeeded @ react-dom.js?ver=16.13.1:826
dispatchDiscreteEvent @ react-dom.js?ver=16.13.1:4290
react-dom.js?ver=16.13.1:82 Warning: unstable_flushDiscreteUpdates: Cannot flush updates when React is already rendering.
    in Unknown (created by WithSelect(WithDispatch(AutosaveMonitor)))
    in WithSelect(WithDispatch(AutosaveMonitor)) (created by LocalAutosaveMonitor)
    in LocalAutosaveMonitor (created by IfCondition(LocalAutosaveMonitor))
    in IfCondition(LocalAutosaveMonitor) (created by Layout)
    in Layout (created by Editor)
    in ErrorBoundary (created by Editor)
    in BlockEditorProvider
    in Unknown (created by Context.Consumer)
    in WithRegistryProvider(BlockEditorProvider) (created by EditorProvider)
    in BlockContextProvider (created by EditorProvider)
    in EntityProvider (created by EditorProvider)
    in EntityProvider (created by EditorProvider)
    in EditorProvider
    in Unknown (created by Context.Consumer)
    in WithRegistryProvider(EditorProvider) (created by Editor)
    in DropZoneContextProvider (created by Editor)
    in slot_fill_provider_SlotFillProvider (created by SlotFillProvider)
    in SlotFillProvider (created by Editor)
    in StrictMode (created by Editor)
    in Editor

The error in OP still persists, but i found out that i dont even need to touch anything, so im guessing it occurs during load (error shows up after 5-6 seconds)